Systems and methods for treating spinal pain

ABSTRACT

The present invention provides systems and methods for selectively applying electrical energy to a fissure or tear location within an invertebral disc. The present invention applies high frequency (RF) electrical energy to one or more active electrodes in the presence of electrically conductive fluid to heat and seal a fissure on an annulus fibrosus. In one aspect of the invention, a method is provided for treating the fissure by applying sufficient electrical energy to the disc tissue to seal the fissure. In one embodiment, the RF energy is directed through the conductive fluid to heat the tissue immediately surrounding the fissure. The RF energy is sufficient to vaporize at least a portion of the fluid in contact with the active electrode. In another embodiment, the electrical current is directed through the tissue to directly heat the annulus tissue. This causes the annulus tissue to contract and seal the fissure. In a specific configuration, a sealant is added to the fissure to enhance the seal.

RELATED APPLICATIONS

The present application derives priority from U.S. ProvisionalApplication No. 60/159,244 filed Oct. 13, 1999 which is acontinuation-in-part of U.S. patent application Ser. No. 09/026,851, nowU.S. Pat. No. 6,277,112 and Ser. No. 09/026,698, both filed Feb. 20,1998, which are continuation-in-parts of U.S. patent application Ser.No. 08/690,159, filed Jul. 16, 1996, now U.S. Pat. No. 5,902,272.

This application is also a continuation-in-part of U.S. patentapplication Ser. No. 09/316,472, filed May 21, 1999, now U.S. Pat. No.6,264,650, which is a continuation-in-part of U.S. patent applicationSer. No. 09/295,687, filed Apr. 21, 1999, now U.S. Pat. No. 6,203,542,U.S. patent application Ser. No. 09/054,323, filed Apr. 2, 1998, nowU.S. Pat. No. 6,063,019, and U.S. patent application Ser. No.09/268,616, filed Mar. 15, 1999, now U.S. Pat. No. 6,159,208, thecomplete disclosures of which are incorporated herein by reference forall purposes.

This application also derives priority from U.S. patent application Ser.No. 08/942,580 filed on Oct. 2, 1997, now U.S. Pat. No. 6,159,194, andU.S. patent application Ser. No. 08/990,374, filed on Dec. 15, 1997, nowU.S. Pat. No. 6,109,268, the complete disclosures of which areincorporated herein by reference for all purposes.

The present invention is related to commonly assigned Provisional PatentApplication Nos. 60/062,996 and 60/062,997, non-provisional U.S. patentapplication Ser. No. 08/970,239, filed Nov. 14, 1997, and Ser. No.08/977,845, filed on Nov. 25, 1997, U.S. application Ser. No.08/753,227, filed on Nov. 22, 1996, and PCT International Application,U.S. National Phase Serial No. PCT/US94/05168, filed on May 10, 1994,now U.S. Pat. No. 5,697,281, which was a continuation-in-part ofapplication Ser. No. 08/059,681, filed on May 10, 1993, which was acontinuation-in-part of application Ser. No. 07/958,977, filed on Oct.9, 1992, which was a continuation-in-part of application Ser. No.07/817,575, filed on Jan. 7, 1992, the complete disclosures of which areincorporated herein by reference for all purposes. The present inventionis also related to commonly assigned U.S. Pat. No. 5,683,366, filed Nov.22, 1995, and U.S. Pat. No. 5,697,536, filed on Jun. 2, 1995, thecomplete disclosures of which are incorporated herein by reference forall purposes.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of electrosurgery,and more particularly to surgical devices and methods which employ highfrequency electrical energy to treat tissue in regions of the spine. Thepresent invention is particularly suited for the treatment of fissuresin discs.

The major causes of persistent, often disabling, back pain aredisruption of the disc annulus, chronic inflammation of the disc (e.g.,herniation), or relative instability of the vertebral bodies surroundinga given disc, such as the instability that often occurs due to adegenerative disease. Spinal discs mainly function to cushion and tetherthe vertebrae, providing flexibility and stability to the patient'sspine. Spinal discs comprise a central hydrostatic cushion, the nucleuspulposus, surrounded by a multi-layered ligament, the annulus fibrosis.As discs degenerate, they lose their water content and height whichbrings the vertebrae closer together. This results in a weakening of theshock absorption properties of the disc and a narrowing of the nerveopenings in the sides of the spine which may pinch the nerve. This discdegeneration can eventually cause back and leg pain. Weakness in theannulus from degenerative discs or disc injury can allow fragments ofnucleus pulposus from within the disc space to migrate into the spinalcanal. There, displaced nucleus or protrusion of annulus fibrosis, e.g.,herniation, may impinge on spinal nerves. The mere proximity of thenucleus pulposus or a damaged annulus to a nerve can cause directpressure against the nerve, resulting in numbness and weakness of legmuscles.

Often, inflammation from disc herniation can be treated successfully bynon-surgical means, such as rest, therapeutic exercise, oralanti-inflammatory medications or epidural injection of corticosteroids.In some cases, the disc tissue is irreparably damaged, therebynecessitating removal of a portion of the disc or the entire disc toeliminate the source of inflammation and pressure. In more severe cases,the adjacent vertebral bodies must be stabilized following excision ofthe disc material to avoid recurrence of the disabling back pain. Oneapproach to stabilizing the vertebrae, termed spinal fusion, is toinsert an interbody graft or implant into the space vacated by thedegenerative disc. In this procedure, a small amount of bone may begrafted from other portions of the body, such as the hip, and packedinto the implants. This allows the bone to grow through and around theimplant, fusing the vertebral bodies and alleviating the pain.

Until recently, spinal discectomy and fusion procedures resulted inmajor operations and traumatic dissection of muscle and bone removal orbone fusion. To overcome the disadvantages of traditional traumaticspine surgery, minimally invasive spine surgery was developed. Inendoscopic spinal procedures, the spinal canal is not violated andtherefore epidural bleeding with ensuring scarring is minimized orcompletely avoided. In addition, the risk of instability from ligamentand bone removal is generally lower in endoscopic procedures than withopen discectomy. Further, more rapid rehabilitation facilitates fasterrecovery and return to work.

Minimally invasive techniques for the treatment of spinal diseases ordisorders include chemonucleolysis, laser techniques and mechanicaltechniques. These procedures generally require the surgeon to form apassage or operating corridor from the external surface of the patientto the spinal disc(s) for passage of surgical instruments, implants andthe like. Typically, the formation of this operating corridor requiresthe removal of soft tissue, muscle or other types of tissue depending onthe procedure (i.e., laparascopic, thoracoscopic, arthroscopic, back,etc.). This tissue is usually removed with mechanical instruments, suchas pituitary rongeurs, curettes, graspers, cutters, drills,microdebriders and the like. Unfortunately, these mechanical instrumentsgreatly lengthen and increase the complexity of the procedure. Inaddition, these instruments sever blood vessels within this tissue,usually causing profuse bleeding that obstructs the surgeon's view ofthe target site.

Once the operating corridor is established, the nerve root is retractedand a portion or all of the disc is removed with mechanical instruments,such as a pituitary rongeur. In addition to the above problems withmechanical instruments, there are serious concerns because theseinstruments are not precise, and it is often difficult, during theprocedure, to differentiate between the target disc tissue, and otherstructures within the spine, such as bone, cartilage, ligaments, nervesand non-target tissue. Thus, the surgeon must be extremely careful tominimize damage to the cartilage and bone within the spine, and to avoiddamaging nerves, such as the spinal nerves and the dura matersurrounding the spinal cord.

Lasers were initially considered ideal for spine surgery because lasersablate or vaporize tissue with heat, which also acts to cauterize andseal the small blood vessels in the tissue. Unfortunately, lasers areboth expensive and somewhat tedious to use in these procedures. Anotherdisadvantage with lasers is the difficulty in judging the depth oftissue ablation. Since the surgeon generally points and shoots the laserwithout contacting the tissue, he or she does not receive any tactilefeedback to judge how deeply the laser is cutting. Because healthytissue, bones, ligaments and spinal nerves often lie within closeproximity of the spinal disc, it is essential to maintain a minimumdepth of tissue damage, which cannot always be ensured with a laser.Monopolar radiofrequency devices have been used in limited roles inspine surgery, such as to cauterize severed vessels to improvevisualization. These monopolar devices, however, suffer from thedisadvantage that the electric current will flow through undefined pathsin the patient's body, thereby increasing the risk of unwantedelectrical stimulation to portions of the patient's body. In addition,since the defined path through the patient's body has a relatively highimpedance (because of the large distance or resistivity of the patient'sbody), large voltage differences must typically be applied between thereturn and active electrodes in order to generate a current suitable forablation or cutting of the target tissue. This current, however, mayinadvertently flow along body paths having less impedance than thedefined electrical path, which will substantially increase the currentflowing through these paths, possibly causing damage to or destroyingsurrounding tissue or neighboring peripheral nerves.

SUMMARY OF THE INVENTION

The present invention provides systems, apparatus and methods forselectively applying electrical energy to structures within a patient'sbody, such as tissue within or around the spine. The systems and methodsof the present invention are particularly useful for ablation,resection, aspiration, collagen shrinkage, tissue bonding and/orhemostasis of tissue and other body structures in open and endoscopicspine surgery.

In one aspect of the invention, a method is provided for treating andsealing invertebrate discs which have tears or fissures on the annulusfibrosus. Specifically, the method of the present invention comprisesintroducing an electrosurgical probe to the outer surface of an annulusin close proximity to or in contact with a fissure in the annulus. Highfrequency voltage can then be applied between one or more activeelectrode(s) and one or more return electrode(s) to apply sufficientenergy to the disc tissue to substantially seal the fissure on theannulus. The high frequency voltage will be directed only to the tissueimmediately surrounding the fissure so as to reduce collateral heatingand damage to the annulus tissue and nucleus pulposus.

In a specific configuration, electrically conducting fluid, such asisotonic saline, is directed to the target site, preferably between thefissure and the active electrode. In monopolar embodiments, theconductive fluid will typically be delivered such that the fluidsubstantially surrounds the active electrode, and provides a layer offluid between the active electrode and the tissue. In bipolarembodiments, the conductive fluid preferably generates a current flowpath between the active electrode(s) and one or more returnelectrode(s). The current flow path may be generated by directing anelectrically conducting fluid along a fluid path past the returnelectrode and to the fissure, or by locating a viscous electricallyconducting fluid, such as a gel, at the fissure, and submersing theactive electrode(s) and the return electrode(s) within the conductivegel.

The fissure may be heated either by passing the electric current throughthe tissue to a selected depth before the current returns to the returnelectrode(s) and/or by heating the electrically conducting fluid incontact with the fissure. In the latter embodiment, the electric currentmay not pass into the tissue surrounding the fissure at all. In bothembodiments, the heated fluid and/or the electric current elevates thetemperature of the annulus tissue surrounding the fissure sufficientlyto cause sealing of the fissure. The high frequency voltage is appliedto the active electrode(s) to elevate the temperature of tissueimmediately surrounding the fissure from body temperature (about 37° C.)to a tissue temperature in the range of about 45° C. to 90° C., usuallyabout 60° C. to 70° C., to seal the fissure.

In another aspect, the present invention provides a method of treating afissure. A sealant or bonding material, such as a fibrogen glue orcollagen, is delivered to the fissure. The sealant can be heated so asto seal the fissure.

In a specific configuration, the sealant is directed through a tube or acatheter and onto the fissure. The tube can be disposed within the probeor a separate instrument. An opening or a plurality of openings can bedisposed near the distal end of the tube or along the lumen of the tubeto deliver the sealant from the tube to the fissure. After the sealanthas been delivered to the fissure, high frequency energy, such as RF,can be delivered to heat the sealant to a specified temperature toharden and cover the fissure. Preferably, the high frequency energy canbe applied in a sufficient amount to effectively cause the sealant toharden while avoiding damage to the surrounding tissue.

In another aspect, the present invention provides an electrosurgicalapparatus for treating a fissure in the annulus. The apparatus comprisesan elongate shaft having a proximal end portion and a distal endportion. An active electrode is disposed on the distal end portion ofthe shaft. The apparatus further comprises a return electrode and a highfrequency voltage source which can generate a voltage sufficient to sealthe fissure.

The probe will typically have a suitable diameter and length to allowthe surgeon to reach the fissure by delivering the shaft through apercutaneous penetration in the thoracic cavity, the abdomen, the back,or the like. The shaft of the probe may be rigid or flexible. In mostembodiments, however, the shaft of the probe is semi-flexible orcatheter like so as to permit the treating physician to direct theelectrode from a proximal end of the shaft to the target disc.Alternatively, in any of the embodiments, the probe may be introducedthrough a percutaneous penetration in the body and to the target discthrough a rigid external tube or a trocar cannula. A trephine or otherconventional instrument may be used to form a channel from the trocarcannula through the annulus fibrosus and into the nucleus pulposus.

The probe of the present invention may use a single active electrode oran electrode array distributed over a contact surface of a probe. Theelectrode array usually includes a plurality of independentlycurrent-limited and/or power-controlled active electrodes to applyelectrical energy selectively to the target tissue while limiting theunwanted application of electrical energy to the surrounding tissue andenvironment resulting from power dissipation into surroundingelectrically conductive liquids, such as blood, normal saline,electrically conductive gel and the like.

In a specific configuration the active electrodes are disposed in alinear arrangement near or at the distal end of the probe so as todefine an edge which can promote localized electric fields between theedge and the fissure. The use of the linear electrodes increase theelectric field intensity and reduce the extent or depth of tissueheating as a consequence of the divergence of current flux lines whichemanate from the exposed surface of each active electrode. The linearelectrodes provide an interface which can engage an approximately linearfissure and focus the electrical energy directly to the tissue withinthe fissure. As a result, the linear arrangement can improve the sealingof the fissure and reduce the collateral damage to the surroundingtissue.

In an exemplary embodiment of the apparatus, the return electrode isdisposed on the shaft and spaced apart from the active electrode. Anelectrical current is passed between the active electrode and the returnelectrode. In alternate embodiments the return electrode is a dispersivepad, and the electrical current is passed directly through a patient'stissue.

In another exemplary embodiment, the system further comprises a fluiddelivery element for supplying electrically conductive fluid to thefissure to substantially surround at least the active electrode withelectrically conductive fluid and to locate electrically conductivefluid between the active electrode and the fissure. The fluid deliveryelement may be located on the probe, e.g., a fluid lumen or tube, or itmay be part of a separate instrument. A high frequency voltage sourcegenerates a voltage sufficient to seal the fissure. The electricallyconducting fluid will preferably generate a current flow path betweenthe active electrode(s) and one or more return electrode(s). In aspecific configuration, the return electrode is located on the probe andspaced a sufficient distance from the active electrode(s) tosubstantially avoid or minimize current shorting therebetween and toshield the return electrode from tissue at the target site.

In another aspect, the present invention may be used to both ablate orshrink a portion of the nucleus pulposus, to reduce the water content ofthe nucleus pulposus which will reduce the pressure of the nucleuspulposus on the annulus. In one embodiment, the RF energy heats thetissue directly by virtue of the electrical current flow therethrough,and/or indirectly through the exposure of the tissue to fluid heated byRF energy, to elevate the tissue temperature from normal bodytemperatures (e.g. 37° C.) to temperatures in the range of 45° C. to 90°C., preferably in the range from about 60° C. to 70° C.

The system and methods of the present invention may optionally include atemperature controller coupled to one or more temperature sensors at ornear the distal end of the probe. The controller adjusts the outputvoltage of the power supply in response to a temperature set point andthe measured temperature value. The temperature sensor may be, forexample, a thermocouple, located in the insulating support that measuresa temperature at the distal end of the probe. In this embodiment, thetemperature set point will preferably be one that corresponds to atissue temperature that results, for example, in the contraction of thecollagen tissue, i.e., about 60° C. to 70° C. Alternatively, thetemperature sensor may directly measure the tissue temperature (e.g.,infrared sensor).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an electrosurgical system incorporatinga power supply and an electrosurgical probe for tissue ablation,resection, incision, contraction and for vessel hemostasis according tothe present invention;

FIG. 2 is a side view of an electrosurgical probe according to thepresent invention;

FIG. 3 is a cross-sectional view of a distal portion of the probe ofFIG. 2;

FIG. 4 is an end view of the probe of FIG. 2, illustrating an array ofactive electrodes;

FIG. 5 is an exploded view of the electrical connections within theprobe of FIG. 2;

FIGS. 6-10 are end views of alternative embodiments of the probe of FIG.2, incorporating aspiration electrode(s);

FIGS. 11A-11C illustrate an alternative embodiment incorporating a meshelectrode for ablating aspirated tissue fragments;

FIGS. 12-15 illustrate a method of performing a microendoscopicdiscectomy according to the principles of the present invention;

FIG. 16 is a schematic view of the proximal portion of anotherelectrosurgical system for endoscopic spine surgery incorporating anelectrosurgical instrument according to the present invention;

FIG. 17 is an enlarged view of a distal portion of the electrosurgicalinstrument of FIG. 16;

FIG. 18 illustrates a method of ablating a volume of tissue from thenucleus pulposus of a herniated disc with the electrosurgical system ofFIG. 16;

FIG. 19 illustrates a planar ablation probe for ablating tissue inconfined spaces within a patient's body according to the presentinvention;

FIG. 20 illustrates a distal portion of the planar ablation probe ofFIG. 19;

FIG. 21A is a front sectional view of the planar ablation probe,illustrating an array of semi-cylindrical active electrodes;

FIG. 21B is a front sectional view of an alternative planar ablationprobe, illustrating an array of active electrodes having oppositepolarities;

FIG. 22 is a top, partial section, view of the working end of the planarablation probe of FIG. 19;

FIG. 23 is a side cross-sectional view of the working end of the planarablation probe, illustrating the electrical connection with one of theactive electrodes of FIG. 22;

FIG. 24 is a side cross-sectional view of the proximal end of the planarablation probe, illustrating the electrical connection with a powersource connector;

FIG. 25 is a schematic view illustrating the ablation of meniscus tissuelocated close to articular cartilage between the tibia and femur of apatient with the ablation probe of FIG. 19;

FIG. 26 is an enlarged view of the distal portion of the planar ablationprobe, illustrating ablation or cutting of meniscus tissue;

FIG. 27 illustrates a method of ablating tissue with a planar ablationprobe incorporating a single active electrode;

FIG. 28 is a schematic view illustrating the ablation of soft tissuefrom adjacent surfaces of the vertebrae with the planar ablation probeof the present invention;

FIG. 29 is a perspective view of an alternative embodiment of the planarablation probe incorporating a ceramic support structure with conductivestrips printed thereon;

FIG. 30 is a top partial cross-sectional view of the planar ablationprobe of FIG. 29;

FIG. 31 is an end view of the probe of FIG. 30;

FIGS. 32A and 32B illustrate an alternative cage aspiration electrodefor use with the electrosurgical probes shown in FIGS. 2-11;

FIGS. 33A-33C illustrate an alternative dome shaped aspiration electrodefor use with the electrosurgical probes of FIGS. 2-11;

FIGS. 34-36 illustrates another system and method of the presentinvention for percutaneously contracting collagen fibers within a spinaldisc with a small, needle-sized instrument.

FIG. 37 is a partial cross-section of an intervertebral disc havingfissures on the inner surface and outer surfaces thereof;

FIG. 38 illustrates a method of sealing a fissure on the outer surfaceof the annulus of the disc;

FIG. 39 illustrates a method of sealing a fissure on the inner surfaceof the annulus disc; and

FIG. 40 illustrates one embodiment of a device for sealing a fissure inthe annulus;

DESCRIPTION OF SPECIFIC EMBODIMENTS

The present invention provides systems and methods for selectivelyapplying electrical energy to a target location within or on a patient'sbody, particularly including tissue or other body structures in thespine. These procedures include laminectomy/discectomy procedures fortreating herniated disks, decompressive laminectomy for stenosis in thelumbosacral and cervical spine, medial facetectomy, posteriorlumbosacral and cervical spine fusions, treatment of scoliosisassociated with vertebral disease, foraminotomies to remove the roof ofthe intervertebral foramina to relieve nerve root compression andanterior cervical and lumbar diskectomies. These procedures may beperformed through open procedures, or using minimally invasivetechniques, such as thoracoscopy, arthroscopy, laparascopy or the like.

In the present invention, high frequency (RF) electrical energy isapplied to one or more active electrodes in the presence of electricallyconductive fluid to remove and/or modify the structure of tissuestructures. Depending on the specific procedure, the present inventionmay be used to: (1) volumetrically remove tissue, bone, ligament orcartilage (i.e., ablate or effect molecular dissociation of the bodystructure); (2) cut or resect tissue or other body structures; (3)shrink or contract collagen connective tissue; (4) coagulate severedblood vessels; and/or (5) seal fissures or other openings

In some procedures, e.g., shrinkage of nucleus pulposus in herniateddiscs, it is desired to shrink or contract collagen connective tissue atthe target site. In these procedures, the RF energy heats the tissuedirectly by virtue of the electrical current flow therethrough, and/orindirectly through the exposure of the tissue to fluid heated by RFenergy, to elevate the tissue temperature from normal body temperatures(e.g., 37° C.) to temperatures in the range of 45° C. to 90° C.,preferably in the range from about 60° C. to 70° C. Thermal shrinkage ofcollagen fibers occurs within a small temperature range which, formammalian collagen is in the range from 60° C. to 70° C. (Deak, G., etal., “The Thermal Shrinkage Process of Collagen Fibres as Revealed byPolarization Optical Analysis of Topooptical Staining Reactions,” ActaMorphologica Acad. Sci. of Hungary, Vol. 15(2), pp. 195-208, 1967).Collagen fibers typically undergo thermal shrinkage in the range of 60°C. to about 70° C. Previously reported research has attributed thermalshrinkage of collagen to the cleaving of the internal stabilizingcross-linkages within the collagen matrix (Deak, ibid). It has also beenreported that when the collagen temperature is increased above 70° C.,the collagen matrix begins to relax again and the shrinkage effect isreversed resulting in no net shrinkage (Allain, J. C., et al.,“Isometric Tensions Developed During the Hydrothermal Swelling of RatSkin,” Connective Tissue Research, Vol. 7, pp. 127-133, 1980).Consequently, the controlled heating of tissue to a precise depth iscritical to the achievement of therapeutic collagen shrinkage. A moredetailed description of collagen shrinkage can be found in U.S. patentapplication Ser. No. 08/942,580, filed Oct. 2, 1997, previouslyincorporated herein by reference.

The preferred depth of heating to effect the shrinkage of collagen inthe heated region (i.e., the depth to which the tissue is elevated totemperatures between 60° C. to 70° C.) generally depends on (1) thethickness of the tissue, (2) the location of nearby structures (e.g.,nerves) that should not be exposed to damaging temperatures, and/or (3)the volume of contraction desired to relieve pressure on the spinalnerve. The depth of heating is usually in the range from 0 to 3.5 mm. Inthe case of collagen within the nucleus pulposus, the depth of heatingis preferably in the range from about 0 to about 2.0 mm.

In another method of the present invention, the tissue structures arevolumetrically removed or ablated. In this procedure, a high frequencyvoltage difference is applied between one or more active electrode(s)and one or more return electrode(s) to develop high electric fieldintensities in the vicinity of the target tissue site. The high electricfield intensities lead to electric field induced molecular breakdown oftarget tissue through molecular dissociation (rather than thermalevaporation or carbonization). Applicant believes that the tissuestructure is volumetrically removed through molecular disintegration oflarger organic molecules into smaller molecules and/or atoms, such ashydrogen, oxides of carbon, hydrocarbons and nitrogen compounds. Thismolecular disintegration completely removes the tissue structure, asopposed to dehydrating the tissue material by the removal of liquidwithin the cells of the tissue, as is typically the case withelectrosurgical desiccation and vaporization.

The high electric field intensities may be generated by applying a highfrequency voltage that is sufficient to vaporize an electricallyconducting fluid over at least a portion of the active electrode(s) inthe region between the distal tip of the active electrode(s) and thetarget tissue. The electrically conductive fluid may be a gas or liquid,such as isotonic saline, delivered to the target site, or a viscousfluid, such as a gel, that is located at the target site. In the latterembodiment, the active electrode(s) are submersed in the electricallyconductive gel during the surgical procedure. Since the vapor layer orvaporized region has a relatively high electrical impedance, itincreases the voltage differential between the active electrode tip andthe tissue and causes ionization within the vapor layer due to thepresence of an ionizable species (e.g., sodium when isotonic saline isthe electrically conducting fluid). This ionization, under optimalconditions, induces the discharge of energetic electrons and photonsfrom the vapor layer and to the surface of the target tissue. Thisenergy may be in the form of energetic photons (e.g., ultravioletradiation), energetic particles (e.g., electrons) or a combinationthereof. A more detailed description of this cold ablation phenomena,termed Coblation™, can be found in commonly assigned U.S. Pat. No.5,683,366 the complete disclosure of which is incorporated herein byreference.

The present invention applies high frequency (RF) electrical energy inan electrically conducting fluid environment to remove (i.e., resect,cut or ablate) or contract a tissue structure, and to seal transectedvessels within the region of the target tissue. The present invention isparticularly useful for sealing larger arterial vessels, e.g., on theorder of 1 mm or greater. In some embodiments, a high frequency powersupply is provided having an ablation mode, wherein a first voltage isapplied to an active electrode sufficient to effect moleculardissociation or disintegration of the tissue, and a coagulation mode,wherein a second, lower voltage is applied to an active electrode(either the same or a different electrode) sufficient to achievehemostasis of severed vessels within the tissue. In other embodiments,an electrosurgical probe is provided having one or more coagulationelectrode(s) configured for sealing a severed vessel, such as anarterial vessel, and one or more active electrodes configured for eithercontracting the collagen fibers within the tissue or removing (ablating)the tissue, e.g., by applying sufficient energy to the tissue to effectmolecular dissociation. In the latter embodiments, the coagulationelectrode(s) may be configured such that a single voltage can be appliedto coagulate with the coagulation electrode(s), and to ablate orcontract with the active electrode(s). In other embodiments, the powersupply is combined with the coagulation probe such that the coagulationelectrode is used when the power supply is in the coagulation mode (lowvoltage), and the active electrode(s) are used when the power supply isin the ablation mode (higher voltage).

In the method of the present invention, one or more active electrodesare brought into close proximity to tissue at a target site, and thepower supply is activated in the ablation mode such that sufficientvoltage is applied between the active electrodes and the returnelectrode to volumetrically remove the tissue through moleculardissociation, as described below. During this process, vessels withinthe tissue will be severed. Smaller vessels will be automatically sealedwith the system and method of the present invention. Larger vessels, andthose with a higher flow rate, such as arterial vessels, may not beautomatically sealed in the ablation mode. In these cases, the severedvessels may be sealed by activating a control (e.g., a foot pedal) toreduce the voltage of the power supply into the coagulation mode. Inthis mode, the active electrodes may be pressed against the severedvessel to provide sealing and/or coagulation of the vessel.Alternatively, a coagulation electrode located on the same or adifferent probe may be pressed against the severed vessel. Once thevessel is adequately sealed, the surgeon activates a control (e.g.,another foot pedal) to increase the voltage of the power supply backinto the ablation mode.

The present invention is particularly useful for removing or ablatingtissue around nerves, such as spinal or cranial nerves, e.g., the spinalcord and the surrounding dura mater. One of the significant drawbackswith the prior art cutters, graspers, and lasers is that these devicesdo not differentiate between the target tissue and the surroundingnerves or bone. Therefore, the surgeon must be extremely careful duringthese procedures to avoid damage to the bone or nerves within and aroundthe spinal cord. In the present invention, the Coblation™ process forremoving tissue results in extremely small depths of collateral tissuedamage as discussed above. This allows the surgeon to remove tissueclose to a nerve without causing collateral damage to the nerve fibers.

In addition to the generally precise nature of the novel mechanisms ofthe present invention, applicant has discovered an additional method ofensuring that adjacent nerves are not damaged during tissue removal.According to the present invention, systems and methods are provided fordistinguishing between the fatty tissue immediately surrounding nervefibers and the normal tissue that is to be removed during the procedure.Nerves usually comprise a connective tissue sheath, or endoneurium,enclosing the bundles of nerve fibers to protect these nerve fibers.This protective tissue sheath typically comprises a fatty tissue (e.g.,adipose tissue) having substantially different electrical propertiesthan the normal target tissue, such as the disc and other surroundingtissue that are, for example, removed from the spine during spinalprocedures. The system of the present invention measures the electricalproperties of the tissue at the tip of the probe with one or more activeelectrode(s). These electrical properties may include electricalconductivity at one, several or a range of frequencies (e.g., in therange from 1 kHz to 100 MHz), dielectric constant, capacitance orcombinations of these. In this embodiment, an audible signal may beproduced when the sensing electrode(s) at the tip of the probe detectsthe fatty tissue surrounding a nerve, or direct feedback control can beprovided to only supply power to the active electrode(s) eitherindividually or to the complete array of electrodes, if and when thetissue encountered at the tip or working end of the probe is normaltissue based on the measured electrical properties.

In one embodiment, the current limiting elements (discussed in detailabove) are configured such that the active electrodes will shut down orturn off when the electrical impedance reaches a threshold level. Whenthis threshold level is set to the impedance of the fatty tissuesurrounding nerves, the active electrodes will shut off whenever theycome in contact with, or in close proximity to, nerves. Meanwhile, theother active electrodes, which are in contact with or in close proximityto nasal tissue, will continue to conduct electric current to the returnelectrode. This selective ablation or removal of lower impedance tissuein combination with the Coblation® mechanism of the present inventionallows the surgeon to precisely remove tissue around nerves or bone.

In addition to the above, applicant has discovered that the Coblation®mechanism of the present invention can be manipulated to ablate orremove certain tissue structures, while having little effect on othertissue structures. As discussed above, the present invention uses atechnique of vaporizing electrically conductive fluid to form a plasmalayer or pocket around the active electrode(s), and then inducing thedischarge of energy from this plasma or vapor layer to break themolecular bonds of the tissue structure. Based on initial experiments,applicants believe that the free electrons within the ionized vaporlayer are accelerated in the high electric fields near the electrodetip(s). When the density of the vapor layer (or within a bubble formedin the electrically conducting liquid) becomes sufficiently low (i.e.,less than approximately 10²⁰ atoms/cm³ for aqueous solutions), theelectron mean free path increases to enable subsequently injectedelectrons to cause impact ionization within these regions of low density(i.e., vapor layers or bubbles). Energy evolved by the energeticelectrons (e.g., 4 to 5 eV) can subsequently bombard a molecule andbreak its bonds, dissociating a molecule into free radicals, which thencombine into final gaseous or liquid species.

The energy evolved by the energetic electrons may be varied by adjustinga variety of factors, such as: the number of active electrodes;electrode size and spacing; electrode surface area; asperities and sharpedges on the electrode surfaces; electrode materials; applied voltageand power; current limiting means, such as inductors; electricalconductivity of the fluid in contact with the electrodes; density of thefluid; and other factors. Accordingly, these factors can be manipulatedto control the energy level of the excited electrons. Since differenttissue structures have different molecular bonds, the present inventioncan be configured to break the molecular bonds of certain tissue, whilehaving too low an energy to break the molecular bonds of other tissue.For example, fatty tissue, (e.g., adipose) tissue has double bonds thatrequire a substantially higher energy level than 4 to 5 eV to break.Accordingly, the present invention in its current configurationgenerally does not ablate or remove such fatty tissue. Of course,factors may be changed such that these double bonds can be broken (e.g.,increasing voltage or changing the electrode configuration to increasethe current density at the electrode tips).

The electrosurgical probe or catheter will comprise a shaft or ahandpiece having a proximal end and a distal end which supports one ormore active electrode(s). The shaft or handpiece may assume a widevariety of configurations, with the primary purpose being tomechanically support the active electrode and permit the treatingphysician to manipulate the electrode from a proximal end of the shaft.The shaft may be rigid or flexible, with flexible shafts optionallybeing combined with a generally rigid external tube for mechanicalsupport. Flexible shafts may be combined with pull wires, shape memoryactuators, and other known mechanisms for effecting selective deflectionof the distal end of the shaft to facilitate positioning of theelectrode array. The shaft will usually include a plurality of wires orother conductive elements running axially therethrough to permitconnection of the electrode array to a connector at the proximal end ofthe shaft.

For endoscopic procedures within the spine, the shaft will have asuitable diameter and length to allow the surgeon to reach the targetsite (e.g., a disc) by delivering the shaft through the thoracic cavity,the abdomen or the like. Thus, the shaft will usually have a length inthe range of about 5.0 to 30.0 cm, and a diameter in the range of about0.2 mm to about 20 mm. Alternatively, the shaft may be delivereddirectly through the patient's back in a posterior approach, which wouldconsiderably reduce the required length of the shaft. In any of theseembodiments, the shaft may also be introduced through rigid or flexibleendoscopes. Specific shaft designs will be described in detail inconnection with the figures hereinafter.

In an alternative embodiment, the probe may comprise a long, thin needle(e.g., on the order of about 1 mm in diameter or less) that can bepercutaneously introduced through the patient's back directly into thespine (see FIGS. 34-36). The needle will include one or more activeelectrode(s) for applying electrical energy to tissues within the spine.The needle may include one or more return electrode(s), or the returnelectrode may be positioned on the patient's back, as a dispersive pad.In either embodiment, sufficient electrical energy is applied throughthe needle to the active electrode(s) to either shrink the collagenfibers within the spinal disk, or to ablate tissue within the disk.

The current flow path between the active electrode(s) and the returnelectrode(s) may be generated by submerging the tissue site in anelectrical conducting fluid (e.g., within a liquid or a viscous fluid,such as an electrically conductive gel) or by directing an electricallyconducting fluid along a fluid path to the target site (i.e., a liquid,such as isotonic saline, or a gas, such as argon). This latter method isparticularly effective in a dry environment (i.e., the tissue is notsubmerged in fluid) because the electrically conducting fluid provides asuitable current flow path from the active electrode to the returnelectrode. A more complete description of an exemplary method ofdirecting electrically conducting fluid between the active and returnelectrodes is described in U.S. Pat. No. 5,697,536, previouslyincorporated herein by reference.

In some procedures, it may also be necessary to retrieve or aspirate theelectrically conductive fluid after it has been directed to the targetsite. In addition, it may be desirable to aspirate small pieces oftissue that are not completely disintegrated by the high frequencyenergy, or other fluids at the target site, such as blood, mucus, thegaseous products of ablation, etc. Accordingly, the system of thepresent invention will usually include a suction lumen in the probe, oron another instrument, for aspirating fluids from the target site. Inaddition, the invention may include one or more aspiration electrode(s)coupled to the distal end of the suction lumen for ablating, or at leastreducing the volume of, non-ablated tissue fragments that are aspiratedinto the lumen. The aspiration electrode(s) function mainly to inhibitclogging of the lumen that may otherwise occur as larger tissuefragments are drawn therein. The aspiration electrode(s) may bedifferent from the ablation active electrode(s), or the sameelectrode(s) may serve both functions. A more complete description ofprobes incorporating aspiration electrode(s) can be found in commonlyassigned, co-pending U.S. patent application Ser. No. 09/010,382, filedJan. 21, 1998, the complete disclosure of which is incorporated hereinby reference.

The present invention may use a single active electrode or an electrodearray distributed over a contact surface of a probe. In the latterembodiment, the electrode array usually includes a plurality ofindependently current-limited and/or power-controlled active electrodesto apply electrical energy selectively to the target tissue whilelimiting the unwanted application of electrical energy to thesurrounding tissue and environment resulting from power dissipation intosurrounding electrically conductive liquids, such as blood, normalsaline, electrically conductive gel and the like. The active electrodesmay be independently current-limited by isolating the electrodes fromeach other and connecting each electrode to a separate power source thatis isolated from the other active electrodes. Alternatively, the activeelectrodes may be connected to each other at either the proximal ordistal ends of the probe to form a single wire that couples to a powersource.

In some embodiments, the active electrode(s) have an active portion orsurface with surface geometries shaped to promote the electric fieldintensity and associated current density along the leading edges of theelectrodes. Suitable surface geometries may be obtained by creatingelectrode shapes that include preferential sharp edges, or by creatingasperities or other surface roughness on the active surface(s) of theelectrodes. Electrode shapes according to the present invention caninclude the use of formed wire (e.g., by drawing round wire through ashaping die) to form electrodes with a variety of cross-sectionalshapes, such as square, rectangular, L or V shaped, or the like.Electrode edges may also be created by removing a portion of theelongate metal electrode to reshape the cross-section. For example,material can be ground along the length of a round or hollow wireelectrode to form D or C shaped wires, respectively, with edges facingin the cutting direction. Alternatively, material can be removed atclosely spaced intervals along the electrode length to form transversegrooves, slots, threads or the like along the electrodes.

Additionally or alternatively, the active electrode surface(s) may bemodified through chemical, electrochemical or abrasive methods to createa multiplicity of surface asperities on the electrode surface. Thesesurface asperities will promote high electric field intensities betweenthe active electrode surface(s) and the target tissue to facilitateablation or cutting of the tissue. For example, surface asperities maybe created by etching the active electrodes with etchants having a Phless than 7.0 or by using a high velocity stream of abrasive particles(e.g., grit blasting) to create asperities on the surface of anelongated electrode.

The active electrode(s) are typically mounted in an electricallyinsulating electrode support that extends from the electrosurgicalprobe. In some embodiments, the electrode support comprises a pluralityof wafer layers bonded together, e.g., by a glass adhesive or the like,or a single wafer. The wafer layer(s) have conductive strips printedthereon to form the active electrode(s) and the return electrode(s). Inone embodiment, the proximal end of the wafer layer(s) will have anumber of holes extending from the conductor strips to an exposedsurface of the wafer layers for connection to electrical conductor leadtraces in the electrosurgical probe or handpiece. The wafer layerspreferably comprise a ceramic material, such as alumina, and theelectrode will preferably comprise a metallic material, such as gold,copper, platinum, palladium, tungsten, silver or the like. Suitablemultilayer ceramic electrodes are commercially available from e.g.,VisPro Corporation of Beaverton, Oreg.

In one configuration, each individual active electrode in the electrodearray is electrically insulated from all other active electrodes in thearray within said probe and is connected to a power source which isisolated from each of the other active electrodes in the array or tocircuitry which limits or interrupts current flow to the activeelectrode when low resistivity material (e.g., blood, electricallyconductive saline irrigant or electrically conductive gel) causes alower impedance path between the return electrode and the individualactive electrode. The isolated power sources for each individual activeelectrode may be separate power supply circuits having internalimpedance characteristics which limit power to the associated activeelectrode when a low impedance return path is encountered. By way ofexample, the isolated power source may be a user selectable constantcurrent source. In this embodiment, lower impedance paths willautomatically result in lower resistive heating levels since the heatingis proportional to the square of the operating current times theimpedance. Alternatively, a single power source may be connected to eachof the active electrodes through independently actuatable switches, orby independent current limiting elements, such as inductors, capacitors,resistors and/or combinations thereof. The current limiting elements maybe provided in the probe, connectors, cable, controller or along theconductive path from the controller to the distal tip of the probe.Alternatively, the resistance and/or capacitance may occur on thesurface of the active electrode(s) due to oxide layers which formselected active electrodes (e.g., titanium or a resistive coating on thesurface of metal, such as platinum).

The tip region of the probe may comprise many independent activeelectrodes designed to deliver electrical energy in the vicinity of thetip. The selective application of electrical energy to the conductivefluid is achieved by connecting each individual active electrode and thereturn electrode to a power source having independently controlled orcurrent limited channels. The return electrode(s) may comprise a singletubular member of conductive material proximal to the electrode array atthe tip which also serves as a conduit for the supply of theelectrically conducting fluid between the active and return electrodes.Alternatively, the probe may comprise an array of return electrodes atthe distal tip of the probe (together with the active electrodes) tomaintain the electric current at the tip. The application of highfrequency voltage between the return electrode(s) and the electrodearray results in the generation of high electric field intensities atthe distal tips of the active electrodes with conduction of highfrequency current from each individual active electrode to the returnelectrode. The current flow from each individual active electrode to thereturn electrode(s) is controlled by either active or passive means, ora combination thereof, to deliver electrical energy to the surroundingconductive fluid while minimizing energy delivery to surrounding(non-target) tissue.

The application of a high frequency voltage between the returnelectrode(s) and the active electrode(s) for appropriate time intervalseffects cutting, removing, ablating, shaping, contracting or otherwisemodifying the target tissue. The tissue volume over which energy isdissipated (i.e., a high current density exists) may be preciselycontrolled, for example, by the use of a multiplicity of small activeelectrodes whose effective diameters or principal dimensions range fromabout 5 mm to 0.01 mm, preferably from about 2 mm to 0.05 mm, and morepreferably from about 1 mm to 0.1 mm. Electrode areas for both circularand non-circular electrodes will have a contact area (per activeelectrode) below 25 mm², preferably being in the range from 0.0001 mm²to 1 mm², and more preferably from 0.005 mm² to 0.5 mm². Thecircumscribed area of the electrode array is in the range from 0.25 mm²to 200 mm², preferably from 0.5 mm² to 100 mm², and will usually includeat least two isolated active electrodes, preferably at least five activeelectrodes, often greater than 10 active electrodes and even 50 or moreactive electrodes, disposed over the distal contact surfaces on theshaft. The use of small diameter active electrodes increases theelectric field intensity and reduces the extent or depth of tissueheating as a consequence of the divergence of current flux lines whichemanate from the exposed surface of each active electrode.

The area of the tissue treatment surface can vary widely, and the tissuetreatment surface can assume a variety of geometries, with particularareas and geometries being selected for specific applications. Activeelectrode surfaces can have areas in the range from 0.25 mm² to 75 mm²,usually being from about 0.5 mm² to 40 mm². The geometries can beplanar, concave, convex, hemispherical, conical, linear “in-line” arrayor virtually any other regular or irregular shape. Most commonly, theactive electrode(s) or active electrode(s) will be formed at the distaltip of the electrosurgical probe shaft, frequently being planar,disk-shaped, or hemispherical surfaces for use in reshaping proceduresor being linear arrays for use in cutting. Alternatively oradditionally, the active electrode(s) may be formed on lateral surfacesof the electrosurgical probe shaft (e.g., in the manner of a spatula),facilitating access to certain body structures in endoscopic procedures.

The electrically conducting fluid should have a threshold conductivityto provide a suitable conductive path between the return electrode(s)and the active electrode(s). The electrical conductivity of the fluid(in units of milliSiemans per centimeter or mS/cm) will usually begreater than 0.2 mS/cm, preferably will be greater than 2 mS/cm and morepreferably greater than 10 mS/cm. In an exemplary embodiment, theelectrically conductive fluid is isotonic saline, which has aconductivity of about 17 mS/cm. Alternatively, the fluid may be anelectrically conductive gel or spray, such as a saline electrolyte gel,a conductive ECG spray, an electrode conductivity gel, an ultrasoundtransmission or scanning gel, or the like. Suitable gels or sprays arecommercially available from Graham-Field, Inc of Hauppauge, N.Y.

In some embodiments, the electrode support and the fluid outlet may berecessed from an outer surface of the probe or handpiece to confine theelectrically conductive fluid to the region immediately surrounding theelectrode support. In addition, the shaft may be shaped so as to form acavity around the electrode support and the fluid outlet. This helps toassure that the electrically conductive fluid will remain in contactwith the active electrode(s) and the return electrode(s) to maintain theconductive path therebetween. In addition, this will help to maintain avapor or plasma layer between the active electrode(s) and the tissue atthe treatment site throughout the procedure, which reduces the thermaldamage that might otherwise occur if the vapor layer were extinguisheddue to a lack of conductive fluid. Provision of the electricallyconductive fluid around the target site also helps to maintain thetissue temperature at desired levels.

The voltage applied between the return electrode(s) and the electrodearray will be at high or radio frequency, typically between about 5 kHzand 20 MHz, usually being between about 30 kHz and 2.5 MHz, preferablybeing between about 50 kHz and 500 kHz, more preferably less than 350kHz, and most preferably between about 100 kHz and 200 kHz. The RMS(root mean square) voltage applied will usually be in the range fromabout 5 volts to 1000 volts, preferably being in the range from about 10volts to 500 volts depending on the active electrode size, the operatingfrequency and the operation mode of the particular procedure or desiredeffect on the tissue (i.e., contraction, coagulation or ablation).Typically, the peak-to-peak voltage will be in the range of 10 to 2000volts, preferably in the range of 20 to 1200 volts and more preferablyin the range of about 40 to 800 volts (again, depending on the electrodesize, the operating frequency and the operation mode).

As discussed above, the voltage is usually delivered in a series ofvoltage pulses or alternating current of time varying voltage amplitudewith a sufficiently high frequency (e.g., on the order of 5 kHz to 20MHz) such that the voltage is effectively applied continuously (ascompared with e.g., lasers claiming small depths of necrosis, which aregenerally pulsed about 10 to 20 Hz). In addition, the duty cycle (i.e.,cumulative time in any one-second interval that energy is applied) is onthe order of about 50% for the present invention, as compared withpulsed lasers which typically have a duty cycle of about 0.0001%.

The preferred power source of the present invention delivers a highfrequency current selectable to generate average power levels rangingfrom several milliwatts to tens of watts per electrode, depending on thevolume of target tissue being heated, and/or the maximum allowedtemperature selected for the probe tip. The power source allows the userto select the voltage level according to the specific requirements of aparticular spine procedure, arthroscopic surgery, dermatologicalprocedure, ophthalmic procedures, FESS procedure, open surgery or otherendoscopic surgery procedure. A description of a suitable power sourcecan be found in U.S. Provisional Patent Application No. 60/062,997entitled, filed Oct. 23, 1997, the complete disclosure of which has beenincorporated herein by reference.

The power source may be current limited or otherwise controlled so thatundesired heating of the target tissue or surrounding (non-target)tissue does not occur. In a presently preferred embodiment of thepresent invention, current limiting inductors are placed in series witheach independent active electrode, where the inductance of the inductoris in the range of 10 uH to 50,000 uH, depending on the electricalproperties of the target tissue, the desired tissue heating rate and theoperating frequency. Alternatively, capacitor-inductor (LC) circuitstructures may be employed, as described previously in co-pending PCTapplication No. PCT/US94/05168, the complete disclosure of which isincorporated herein by reference. Additionally, current limitingresistors may be selected. Preferably, these resistors will have a largepositive temperature coefficient of resistance so that, as the currentlevel begins to rise for any individual active electrode in contact witha low resistance medium (e.g., saline irrigant or conductive gel), theresistance of the current limiting resistor increases significantly,thereby minimizing the power delivery from said active electrode intothe low resistance medium (e.g., saline irrigant or conductive gel).

It should be clearly understood that the invention is not limited toelectrically isolated active electrodes, or even to a plurality ofactive electrodes. For example, the array of active electrodes may beconnected to a single lead that extends through the probe shaft to apower source of high frequency current. Alternatively, the probe mayincorporate a single electrode that extends directly through the probeshaft or is connected to a single lead that extends to the power source.The active electrode may have a ball shape (e.g., for tissuevaporization and desiccation), a twizzle shape (for vaporization andneedle-like cutting), a spring shape (for rapid tissue debulking anddesiccation), a twisted metal shape, an annular or solid tube shape orthe like. Alternatively, the electrode may comprise a plurality offilaments, a rigid or flexible brush electrode (for debulking a tumor,such as a fibroid, bladder tumor or a prostate adenoma), a side-effectbrush electrode on a lateral surface of the shaft, a coiled electrode orthe like. In one embodiment, the probe comprises a single activeelectrode that extends from an insulating member, e.g., ceramic, at thedistal end of the probe. The insulating member is preferably a tubularstructure that separates the active electrode from a tubular or annularreturn electrode positioned proximal to the insulating member and theactive electrode.

Referring to FIG. 1, an exemplary electrosurgical system 11 fortreatment of tissue in the spine will now be described in detail.Electrosurgical system 11 generally comprises an electrosurgicalhandpiece or probe 10 connected to a power supply 28 for providing highfrequency voltage to a target site and a fluid source 21 for supplyingelectrically conducting fluid 50 to probe 10. In addition,electrosurgical system 11 may include an endoscope (not shown) with afiber optic head light for viewing the surgical site, particularly inendoscopic spine procedures. The endoscope may be integral with probe10, or it may be part of a separate instrument. The system 11 may alsoinclude a vacuum source (not shown) for coupling to a suction lumen ortube 211 (see FIG. 2) in the probe 10 for aspirating the target site.

As shown, probe 10 generally includes a proximal handle 19 and anelongate shaft 18 having an array 12 of active electrodes 58 at itsdistal end. A connecting cable 34 has a connector 26 for electricallycoupling the active electrodes 58 to power supply 28. The activeelectrodes 58 are electrically isolated from each other and each of theelectrodes 58 is connected to an active or passive control networkwithin power supply 28 by means of a plurality of individually insulatedconductors (not shown). A fluid supply tube 15 is connected to a fluidtube 14 of probe 10 for supplying electrically conducting fluid 50 tothe target site.

Power supply 28 has an operator controllable voltage level adjustment 30to change the applied voltage level, which is observable at a voltagelevel display 32. Power supply 28 also includes first, second and thirdfoot pedals 37, 38, 39 and a cable 36 which is removably coupled topower supply 28. The foot pedals 37, 38, 39 allow the surgeon toremotely adjust the energy level applied to active electrodes 58. In anexemplary embodiment, first foot pedal 37 is used to place the powersupply into the “ablation” mode and second foot pedal 38 places powersupply 28 into the “coagulation” mode. The third foot pedal 39 allowsthe user to adjust the voltage level within the “ablation” mode. In theablation mode, a sufficient voltage is applied to the active electrodesto establish the requisite conditions for molecular dissociation of thetissue (i.e., vaporizing a portion of the electrically conductive fluid,ionizing charged particles within the vapor layer and accelerating thesecharged particles against the tissue). As discussed above, the requisitevoltage level for ablation will vary depending on the number, size,shape and spacing of the electrodes, the distance in which theelectrodes extend from the support member, etc. Once the surgeon placesthe power supply in the “ablation” mode, voltage level adjustment 30 orthird foot pedal 39 may be used to adjust the voltage level to adjustthe degree or aggressiveness of the ablation.

Of course, it will be recognized that the voltage and modality of thepower supply may be controlled by other input devices. However,applicant has found that foot pedals are convenient methods ofcontrolling the power supply while manipulating the probe during asurgical procedure.

In the coagulation mode, the power supply 28 applies a low enoughvoltage to the active electrodes (or the coagulation electrode) to avoidvaporization of the electrically conductive fluid and subsequentmolecular dissociation of the tissue. The surgeon may automaticallytoggle the power supply between the ablation and coagulation modes byalternatively stepping on foot pedals 37, 38, respectively. This allowsthe surgeon to quickly move between coagulation and ablation in situ,without having to remove his/her concentration from the surgical fieldor without having to request an assistant to switch the power supply. Byway of example, as the surgeon is sculpting soft tissue in the ablationmode, the probe typically will simultaneously seal and/or coagulationsmall severed vessels within the tissue. However, larger vessels, orvessels with high fluid pressures (e.g., arterial vessels) may not besealed in the ablation mode. Accordingly, the surgeon can simply step onfoot pedal 38, automatically lowering the voltage level below thethreshold level for ablation, and apply sufficient pressure onto thesevered vessel for a sufficient period of time to seal and/or coagulatethe vessel. After this is completed, the surgeon may quickly move backinto the ablation mode by stepping on foot pedal 37. A specific designof a suitable power supply for use with the present invention can befound in U.S. Provisional Patent Application No. 60/062,997, filed Oct.23, 1997, previously incorporated herein by reference.

FIGS. 2-5 illustrate an exemplary electrosurgical probe 20 constructedaccording to the principles of the present invention. As shown in FIG.2, probe 20 generally includes an elongated shaft 100 which may beflexible or rigid, a handle 204 coupled to the proximal end of shaft 100and an electrode support member 102 coupled to the distal end of shaft100. Shaft 100 preferably comprises a plastic material that is easilymolded into the shape shown in FIG. 2. In an alternative embodiment (notshown), shaft 100 comprises an electrically conducting material, usuallymetal, which is selected from the group comprising tungsten, stainlesssteel alloys, platinum or its alloys, titanium or its alloys, molybdenumor its alloys, and nickel or its alloys. In this embodiment, shaft 100includes an electrically insulating jacket 108, which is typicallyformed as one or more electrically insulating sheaths or coatings, suchas polytetrafluoroethylene, polyimide, and the like. The provision ofthe electrically insulating jacket over the shaft prevents directelectrical contact between these metal elements and any adjacent bodystructure or the surgeon. Such direct electrical contact between a bodystructure (e.g., tendon) and an exposed electrode could result inunwanted heating and necrosis of the structure at the point of contactcausing necrosis.

Handle 204 typically comprises a plastic material that is easily moldedinto a suitable shape for handling by the surgeon. Handle 204 defines aninner cavity (not shown) that houses the electrical connections 250(FIG. 5), and provides a suitable interface for connection to anelectrical connecting cable 22 (see FIG. 1). Electrode support member102 extends from the distal end of shaft 100 (usually about 1 to 20 mm),and provides support for a plurality of electrically isolated activeelectrodes 104 (see FIG. 4). As shown in FIG. 2, a fluid tube 233extends through an opening in handle 204, and includes a connector 235for connection to a fluid supply source, for supplying electricallyconductive fluid to the target site. Fluid tube 233 is coupled to adistal fluid tube 239 that extends along the outer surface of shaft 100to an opening 237 at the distal end of the probe 20, as discussed indetail below. Of course, the invention is not limited to thisconfiguration. For example, fluid tube 233 may extend through a singlelumen (not shown) in shaft 100, or it may be coupled to a plurality oflumens (also not shown) that extend through shaft 100 to a plurality ofopenings at its distal end. Probe 20 may also include a valve 17(FIG. 1) or equivalent structure for controlling the flow rate of theelectrically conducting fluid to the target site.

As shown in FIGS. 3 and 4, electrode support member 102 has asubstantially planar tissue treatment surface 212 and comprises asuitable insulating material (e.g., ceramic or glass material, such asalumina, zirconia and the like) which could be formed at the time ofmanufacture in a flat, hemispherical or other shape according to therequirements of a particular procedure. The preferred support membermaterial is alumina, available from Kyocera Industrial CeramicsCorporation, Elkgrove, Ill., because of its high thermal conductivity,good electrically insulative properties, high flexural modulus,resistance to carbon tracking, biocompatibility, and high melting point.The support member 102 is adhesively joined to a tubular support member(not shown) that extends most or all of the distance between supportmember 102 and the proximal end of probe 20. The tubular memberpreferably comprises an electrically insulating material, such as anepoxy or silicone-based material.

In a preferred construction technique, active electrodes 104 extendthrough pre-formed openings in the support member 102 so that theyprotrude above tissue treatment surface 212 by the desired distance. Theelectrodes are then bonded to the tissue treatment surface 212 ofsupport member 102, typically by an inorganic sealing material. Thesealing material is selected to provide effective electrical insulation,and good adhesion to both the alumina member 102 and the platinum ortitanium active electrodes 104. The sealing material additionally shouldhave a compatible thermal expansion coefficient and a melting point wellbelow that of platinum or titanium and alumina or zirconia, typicallybeing a glass or glass ceramic.

In the embodiment shown in FIGS. 2-5, probe 20 includes a returnelectrode 112 for completing the current path between active electrodes104 and a high frequency power supply 28 (see FIG. 1). As shown, returnelectrode 112 preferably comprises an annular conductive band coupled tothe distal end of shaft 100 slightly proximal to tissue treatmentsurface 212 of electrode support member 102, typically about 0.5 to 10mm and more preferably about 1 to 10 mm. Return electrode 112 is coupledto a connector 258 that extends to the proximal end of probe 10, whereit is suitably connected to power supply 10 (FIG. 1).

As shown in FIG. 2, return electrode 112 is not directly connected toactive electrodes 104. To complete this current path so that activeelectrodes 104 are electrically connected to return electrode 112,electrically conducting fluid (e.g., isotonic saline) is caused to flowtherebetween. In the representative embodiment, the electricallyconducting fluid is delivered through an external fluid tube 239 toopening 237, as described above. Alternatively, the fluid may bedelivered by a fluid delivery element (not shown) that is separate fromprobe 20. In some microendoscopic discectomy procedures, for example,the trocar cannula may be flooded with isotonic saline and the probe 20will be introduced into this flooded cavity. Electrically conductingfluid will be continually resupplied with a separate instrument tomaintain the conduction path between return electrode 112 and activeelectrodes 104.

In alternative embodiments, the fluid path may be formed in probe 20 by,for example, an inner lumen or an annular gap between the returnelectrode and a tubular support member within shaft 100 (not shown).This annular gap may be formed near the perimeter of the shaft 100 suchthat the electrically conducting fluid tends to flow radially inwardtowards the target site, or it may be formed towards the center of shaft100 so that the fluid flows radially outward. In both of theseembodiments, a fluid source (e.g., a bag of fluid elevated above thesurgical site or having a pumping device), is coupled to probe 90 via afluid supply tube (not shown) that may or may not have a controllablevalve. A more complete description of an electrosurgical probeincorporating one or more fluid lumen(s) can be found in parentapplication U.S. Pat. No. 5,697,281, filed on Jun. 7, 1995, the completedisclosure of which has previously been incorporated herein byreference.

Referring to FIG. 4, the electrically isolated active electrodes 104 arespaced apart over tissue treatment surface 212 of electrode supportmember 102. The tissue treatment surface and individual activeelectrodes 104 will usually have dimensions within the ranges set forthabove. In the representative embodiment, the tissue treatment surface212 has a circular cross-sectional shape with a diameter in the range ofabout 1 mm to 30 mm, usually about 2 to 20 mm. The individual activeelectrodes 104 preferably extend outward from tissue treatment surface212 by a distance of about 0.1 to 8 mm, usually about 0.2 to 4 mm.Applicant has found that this configuration increases the high electricfield intensities and associated current densities around activeelectrodes 104 to facilitate the ablation of tissue as described indetail above.

In the embodiment of FIGS. 2-5, the probe includes a single, largeropening 209 in the center of tissue treatment surface 212, and aplurality of active electrodes (e.g., about 3-15) around the perimeterof surface 212 (see FIG. 3). Alternatively, the probe may include asingle, annular, or partially annular, active electrode at the perimeterof the tissue treatment surface. The central opening 209 is coupled to asuction or aspiration lumen 213 (see FIG. 2) within shaft 100 and asuction tube 211 (FIG. 2) for aspirating tissue, fluids and/or gasesfrom the target site. In this embodiment, the electrically conductivefluid generally flows from opening 237 of fluid tube 239 radially inwardpast active electrodes 104 and then back through the central opening 209of support member 102. Aspirating the electrically conductive fluidduring surgery allows the surgeon to see the target site, and itprevents the fluid from flowing into the patient's body, e.g., into thespine, the abdomen or the thoracic cavity. This aspiration should becontrolled, however, so that the conductive fluid maintains a conductivepath between the active electrode(s) and the return electrode.

Of course, it will be recognized that the distal tip of probe may have avariety of different configurations. For example, the probe may includea plurality of openings 209 around the outer perimeter of tissuetreatment surface 212 (this embodiment not shown in the drawings). Inthis embodiment, the active electrodes 104 extend from the center oftissue treatment surface 212 radially inward from openings 209. Theopenings are suitably coupled to fluid tube 233 for deliveringelectrically conductive fluid to the target site, and aspiration lumen213 for aspirating the fluid after it has completed the conductive pathbetween the return electrode 112 and the active electrodes 104.

In some embodiments, the probe 20 will also include one or moreaspiration electrode(s) coupled to the aspiration lumen for inhibitingclogging during aspiration of tissue fragments from the surgical site.As shown in FIG. 6, one or more of the active electrodes 104 maycomprise loop electrodes 140 that extend across distal opening 209 ofthe suction lumen within shaft 100. In the representative embodiment,two of the active electrodes 104 comprise loop electrodes 140 that crossover the distal opening 209. Of course, it will be recognized that avariety of different configurations are possible, such as a single loopelectrode, or multiple loop electrodes having different configurationsthan shown. In addition, the electrodes may have shapes other thanloops, such as the coiled configurations shown in FIGS. 6 and 7.Alternatively, the electrodes may be formed within suction lumenproximal to the distal opening 209, as shown in FIG. 8. The mainfunction of loop electrodes 140 is to ablate portions of tissue that aredrawn into the suction lumen to prevent clogging of the lumen.

Loop electrodes 140 are electrically isolated from the other activeelectrodes 104, which can be referred to hereinafter as the ablationelectrodes 104. Loop electrodes 140 may or may not be electricallyisolated from each other. Loop electrodes 140 will usually extend onlyabout 0.05 to 4 mm, preferably about 0.1 to 1 mm from the tissuetreatment surface of electrode support member 104.

Referring now to FIGS. 7 and 8, alternative embodiments for aspirationelectrodes will now be described. As shown in FIG. 7, the aspirationelectrodes may comprise a pair of coiled electrodes 150 that extendacross distal opening 209 of the suction lumen. The larger surface areaof the coiled electrodes 150 usually increases the effectiveness of theelectrodes 150 on tissue fragments passing through opening 209. In FIG.8, the aspiration electrode comprises a single coiled electrode 152passing across the distal opening 209 of suction lumen. This singleelectrode 152 may be sufficient to inhibit clogging of the suctionlumen. Alternatively, the aspiration electrodes may be positioned withinthe suction lumen proximal to the distal opening 209. Preferably, theseelectrodes are close to opening 209 so that tissue does not clog theopening 209 before it reaches electrodes 154. In this embodiment, aseparate return electrode 156 may be provided within the suction lumento confine the electric currents therein.

Referring to FIG. 10, another embodiment of the present inventionincorporates an aspiration electrode 160 within the aspiration lumen 162of the probe. As shown, the electrode 160 is positioned just proximal ofdistal opening 209 so that the tissue fragments are ablated as theyenter lumen 162. In the representation embodiment, the aspirationelectrode 160 comprises a loop electrode that stretches across theaspiration lumen 162. However, it will be recognized that many otherconfigurations are possible. In this embodiment, the return electrode164 is located outside of the probe as in the previously embodiments.Alternatively, the return electrode(s) may be located within theaspiration lumen 162 with the aspiration electrode 160. For example, theinner insulating coating 163 may be exposed at portions within the lumen162 to provide a conductive path between this exposed portion of returnelectrode 164 and the aspiration electrode 160. The latter embodimenthas the advantage of confining the electric currents to within theaspiration lumen. In addition, in dry fields in which the conductivefluid is delivered to the target site, it is usually easier to maintaina conductive fluid path between the active and return electrodes in thelatter embodiment because the conductive fluid is aspirated through theaspiration lumen 162 along with the tissue fragments.

Referring to FIG. 9, another embodiment of the present inventionincorporates a wire mesh electrode 600 extending across the distalportion of aspiration lumen 162. As shown, mesh electrode 600 includes aplurality of openings 602 to allow fluids and tissue fragments to flowthrough into aspiration lumen 162. The size of the openings 602 willvary depending on a variety of factors. The mesh electrode may becoupled to the distal or proximal surfaces of ceramic support member102. Wire mesh electrode 600 comprises a conductive material, such astitanium, tantalum, steel, stainless steel, tungsten, copper, gold orthe like. In the representative embodiment, wire mesh electrode 600comprises a different material having a different electric potentialthan the active electrode(s) 104. Preferably, mesh electrode 600comprises steel and active electrode(s) comprises tungsten. Applicanthas found that a slight variance in the electrochemical potential ofmesh electrode 600 and active electrode(s) 104 improves the performanceof the device. Of course, it will be recognized that the mesh electrodemay be electrically insulated from active electrode(s) as in previousembodiments.

Referring now to FIGS. 11A-11C, an alternative embodiment incorporatinga metal screen 610 is illustrated. As shown, metal screen 610 has aplurality of peripheral openings 612 for receiving active electrodes104, and a plurality of inner openings 614 for allowing aspiration offluid and tissue through opening 609 of the aspiration lumen. As shown,screen 610 is press fitted over active electrodes 104 and then adheredto shaft 100 of probe 20. Similar to the mesh electrode embodiment,metal screen 610 may comprise a variety of conductive metals, such astitanium, tantalum, steel, stainless steel, tungsten, copper, gold orthe like. In the representative embodiment, metal screen 610 is coupleddirectly to, or integral with, active electrode(s) 104. In thisembodiment, the active electrode(s) 104 and the metal screen 610 areelectrically coupled to each other.

FIGS. 32 and 33 illustrate alternative embodiments of the mesh andscreen aspiration electrodes. As shown in FIG. 32A and 32B, the probemay include a conductive cage electrode 620 that extends into theaspiration lumen 162 (not shown) to increase the effect of the electrodeon aspirated tissue. FIGS. 33A-33C illustrate a dome-shaped screenelectrode 630 that includes one or more anchors 632 (four in therepresentative embodiment) for attaching the screen electrode 630 to aconductive spacer 634. Screen electrode 630 includes a plurality ofholes 631 for allowing fluid and tissue fragments to pass therethroughto aspiration lumen 162. Screen electrode 630 is sized to fit withinopening 609 of aspiration lumen 162 except for the anchors 632 whichinclude holes 633 for receiving active electrodes 104. Spacer 634includes peripheral holes 636 for receiving active electrodes 104 and acentral hole 638 aligned with suction lumen 162. Spacer 634 may furtherinclude insulated holes 640 for electrically isolating screen electrode630 from active electrodes 104. As shown in FIG. 33C, dome-shaped screenelectrode 630 preferably extends distally from the probe shaft 100 aboutthe same distance as the active electrodes 104. Applicant has found thatthis configuration enhances the ablation rate for tissue adjacent toactive electrodes 104, while still maintaining the ability to ablateaspirated tissue fragments passing through screen 630.

FIG. 5 illustrates the electrical connections 250 within handle 204 forcoupling active electrodes 104 and return electrode 112 to the powersupply 28. As shown, a plurality of wires 252 extend through shaft 100to couple electrodes 104 to a plurality of pins 254, which are pluggedinto a connector block 256 for coupling to a connecting cable 22 (FIG.1). Similarly, return electrode 112 is coupled to connector block 256via a wire 258 and a plug 260.

In some embodiments of the present invention, the probe 20 furtherincludes an identification element that is characteristic of theparticular electrode assembly so that the same power supply 28 can beused for different electrosurgical operations. In one embodiment, forexample, the probe 20 includes a voltage reduction element or a voltagereduction circuit for reducing the voltage applied between the activeelectrodes 104 and the return electrode 112. The voltage reductionelement serves to reduce the voltage applied by the power supply so thatthe voltage between the active electrodes and the return electrode islow enough to avoid excessive power dissipation into the electricallyconducting medium and/or ablation of the soft tissue at the target site.The voltage reduction element primarily allows the electrosurgical probe20 to be compatible with other ArthroCare generators that are adapted toapply higher voltages for ablation or vaporization of tissue. Forcontraction of tissue, for example, the voltage reduction element willserve to reduce a voltage of about 100 to 135 volts rms (which is asetting of 1 on the ArthroCare Model 970 and 980 (i.e., 2000)Generators) to about 45 to 60 volts rms, which is a suitable voltage forcontraction of tissue without ablation (e.g., molecular dissociation) ofthe tissue.

Of course, for some procedures in endoscopic spine surgery, the probewill typically not require a voltage reduction element. Alternatively,the probe may include a voltage increasing element or circuit, ifdesired.

In the representative embodiment, the voltage reduction element is adropping capacitor 262 which has first leg 264 coupled to the returnelectrode wire 258 and a second leg 266 coupled to connector block 256.Of course, the capacitor may be located in other places within thesystem, such as in, or distributed along the length of, the cable, thegenerator, the connector, etc. In addition, it will be recognized thatother voltage reduction elements, such as diodes, transistors,inductors, resistors, capacitors or combinations thereof, may be used inconjunction with the present invention. For example, the probe 90 mayinclude a coded resistor (not shown) that is constructed to lower thevoltage applied between return electrode 112 and active electrodes 104to a suitable level for contraction of tissue. In addition, electricalcircuits may be employed for this purpose.

Alternatively or additionally, the cable 22 that couples the powersupply 10 to the probe 90 may be used as a voltage reduction element.The cable has an inherent capacitance that can be used to reduce thepower supply voltage if the cable is placed into the electrical circuitbetween the power supply, the active electrodes and the returnelectrode. In this embodiment, the cable 22 may be used alone, or incombination with one of the voltage reduction elements discussed above,e.g., a capacitor.

In some embodiments, the probe 20 will further include a switch (notshown) or other input that allows the surgeon to couple and decouple theidentification element to the rest of the electronics in the probe 20.For example, if the surgeon would like to use the same probe forablation of tissue and contraction of tissue in the same procedure, thiscan be accomplished by manipulating the switch. Thus, for ablation oftissue, the surgeon will decouple the voltage reduction element from theelectronics so that the full voltage applied by the power source isapplied to the electrodes on the probe. When the surgeon desires toreduce the voltage to a suitable level for contraction of tissue, he/shecouples the voltage reduction element to the electronics to reduce thevoltage applied by the power supply to the active electrodes.

Further, it should be noted that the present invention can be used witha power supply that is adapted to apply a voltage within the selectedrange for treatment of tissue. In this embodiment, a voltage reductionelement or circuitry may not be desired.

The present invention is particularly useful in microendoscopicdiscectomy procedures, e.g., for decompressing a nerve root with alumbar discectomy. As shown in FIGS. 12-15, a percutaneous penetration270 is made in the patients' back 272 so that the superior lamina 274can be accessed. Typically, a small needle (not shown) is used initiallyto localize the disc space level, and a guidewire (not shown) isinserted and advanced under lateral fluoroscopy to the inferior edge ofthe lamina 274. Sequential cannulated dilators 276 are inserted over theguide wire and each other to provide a hole from the incision 220 to thelamina 274. The first dilator may be used to “palpate” the lamina 274,assuring proper location of its tip between the spinous process andfacet complex just above the inferior edge of the lamina 274. As shownin FIG. 13, a tubular retractor 278 is then passed over the largestdilator down to the lamina 274. The dilators 276 are removed,establishing an operating corridor within the tubular retractor 278.

As shown in FIG. 13, an endoscope 280 is then inserted into the tubularretractor 278 and a ring clamp 282 is used to secure the endoscope 280.Typically, the formation of the operating corridor within retractor 278requires the removal of soft tissue, muscle or other types of tissuethat were forced into this corridor as the dilators 276 and retractor278 were advanced down to the lamina 274. This tissue is usually removedwith mechanical instruments, such as pituitary rongeurs, curettes,graspers, cutters, drills, microdebriders and the like. Unfortunately,these mechanical instruments greatly lengthen and increase thecomplexity of the procedure. In addition, these instruments sever bloodvessels within this tissue, usually causing profuse bleeding thatobstructs the surgeon's view of the target site.

According to the present invention, an electrosurgical probe or catheter284 as described above is introduced into the operating corridor withinthe retractor 278 to remove the soft tissue, muscle and otherobstructions from this corridor so that the surgeon can easily accessand visualization the lamina 274. Once the surgeon has reached hasintroduced the probe 284, electrically conductive fluid 285 is deliveredthrough tube 233 and opening 237 to the tissue (see FIG. 2). The fluidflows past the return electrode 112 to the active electrodes 104 at thedistal end of the shaft. The rate of fluid flow is controlled with valve17 (FIG. 1) such that the zone between the tissue and electrode support102 is constantly immersed in the fluid. The power supply 28 is thenturned on and adjusted such that a high frequency voltage difference isapplied between active electrodes 104 and return electrode 112. Theelectrically conductive fluid provides the conduction path (see currentflux lines) between active electrodes 104 and the return electrode 112.

The high frequency voltage is sufficient to convert the electricallyconductive fluid (not shown) between the target tissue and activeelectrode(s)104 into an ionized vapor layer or plasma (not shown). As aresult of the applied voltage difference between active electrode(s) 104and the target tissue (i.e., the voltage gradient across the plasmalayer), charged particles in the plasma (viz., electrons) areaccelerated towards the tissue. At sufficiently high voltagedifferences, these charged particles gain sufficient energy to causedissociation of the molecular bonds within tissue structures. Thismolecular dissociation is accompanied by the volumetric removal (i.e.,ablative sublimation) of tissue and the production of low molecularweight gases, such as oxygen, nitrogen, carbon dioxide, hydrogen andmethane. The short range of the accelerated charged particles within thetissue confines the molecular dissociation process to the surface layerto minimize damage and necrosis to the underlying tissue.

During the process, the gases will be aspirated through opening 209 andsuction tube 211 to a vacuum source. In addition, excess electricallyconductive fluid, and other fluids (e.g., blood) will be aspirated fromthe operating corridor to facilitate the surgeon's view. During ablationof the tissue, the residual heat generated by the current flux lines(typically less than 150° C.), will usually be sufficient to coagulateany severed blood vessels at the site. If not, the surgeon may switchthe power supply 28 into the coagulation mode by lowering the voltage toa level below the threshold for fluid vaporization, as discussed above.This simultaneous hemostasis results in less bleeding and facilitatesthe surgeon's ability to perform the procedure.

Another advantage of the present invention is the ability to preciselyablate soft tissue without causing necrosis or thermal damage to theunderlying and surrounding tissues, nerves or bone. In addition, thevoltage can be controlled so that the energy directed to the target siteis insufficient to ablate the lamina 274 so that the surgeon canliterally clean the tissue off the lamina 274, without ablating orotherwise effecting significant damage to the lamina.

Referring now to FIGS. 14 and 15, once the operating corridor issufficiently cleared, a laminotomy and medial facetectomy isaccomplished either with conventional techniques (e.g., Kerrison punchor a high speed drill) or with the electrosurgical probe 284 asdiscussed above. After the nerve root is identified, medical retractioncan be achieved with a retractor 288, or the present invention can beused to ablate with precision the disc. If necessary, epidural veins arecauterized either automatically or with the coagulation mode of thepresent invention. If an annulotomy is necessary, it can be accomplishedwith a microknife or the ablation mechanism of the present inventionwhile protecting the nerve root with the retractor 288. The herniateddisc 290 is then removed with a pituitary rongeur in a standard fashion,or once again through ablation as described above.

In another embodiment, the electrosurgical probe of the presentinvention can be used to ablate and/or contract soft tissue within thedisc 290 to allow the annulus 292 to repair itself to preventreoccurrence of this procedure. For tissue contraction, a sufficientvoltage difference is applied between the active electrodes 104 and thereturn electrode 112 to elevate the tissue temperature from normal bodytemperatures (e.g., 37° C.) to temperatures in the range of 45° C. to90° C., preferably in the range from 60° C. to 70° C. This temperatureelevation causes contraction of the collagen connective fibers withinthe disc tissue so that the disc 290 withdraws into the annulus 292.

In one method of tissue contraction according to the present invention,an electrically conductive fluid is delivered to the target site asdescribed above, and heated to a sufficient temperature to inducecontraction or shrinkage of the collagen fibers in the target tissue.The electrically conducting fluid is heated to a temperature sufficientto substantially irreversibly contract the collagen fibers, whichgenerally requires a tissue temperature in the range of about 45° C. to90° C., usually about 60° C. to 70° C. The fluid is heated by applyinghigh frequency electrical energy to the active electrode(s) in contactwith the electrically conducting fluid. The current emanating from theactive electrode(s) 104 heats the fluid and generates a jet or plume ofheated fluid, which is directed towards the target tissue. The heatedfluid elevates the temperature of the collagen sufficiently to causehydrothermal shrinkage of the collagen fibers. The return electrode 112draws the electric current away from the tissue site to limit the depthof penetration of the current into the tissue, thereby inhibitingmolecular dissociation and breakdown of the collagen tissue andminimizing or completely avoiding damage to surrounding and underlyingtissue structures beyond the target tissue site. In an exemplaryembodiment, the active electrode(s) 104 are held away from the tissue asufficient distance such that the RF current does not pass into thetissue at all, but rather passes through the electrically conductingfluid back to the return electrode. In this embodiment, the primarymechanism for imparting energy to the tissue is the heated fluid, ratherthan the electric current.

In an alternative embodiment, the active electrode(s) 104 are broughtinto contact with, or close proximity to, the target tissue so that theelectric current passes directly into the tissue to a selected depth. Inthis embodiment, the return electrode draws the electric current awayfrom the tissue site to limit its depth of penetration into the tissue.Applicant has discovered that the depth of current penetration also canbe varied with the electrosurgical system of the present invention bychanging the frequency of the voltage applied to the active electrodeand the return electrode. This is because the electrical impedance oftissue is known to decrease with increasing frequency due to theelectrical properties of cell membranes which surround electricallyconductive cellular fluid. At lower frequencies (e.g., less than 350kHz), the higher tissue impedance, the presence of the return electrodeand the active electrode configuration of the present invention(discussed in detail below) cause the current flux lines to penetrateless deeply resulting in a smaller depth of tissue heating. In anexemplary embodiment, an operating frequency of about 100 to 200 kHz isapplied to the active electrode(s) to obtain shallow depths of collagenshrinkage (e.g., usually less than 1.5 mm and preferably less than 0.5mm).

In another aspect of the invention, the size (e.g., diameter orprincipal dimension) of the active electrodes employed for treating thetissue are selected according to the intended depth of tissue treatment.As described previously in copending patent application PCTInternational Application, U.S. National Phase Serial No.PCT/US94/05168, the depth of current penetration into tissue increaseswith increasing dimensions of an individual active electrode (assumingother factors remain constant, such as the frequency of the electriccurrent, the return electrode configuration, etc.). The depth of currentpenetration (which refers to the depth at which the current density issufficient to effect a change in the tissue, such as collagen shrinkage,irreversible necrosis, etc.) is on the order of the active electrodediameter for the bipolar configuration of the present invention andoperating at a frequency of about 100 kHz to about 200 kHz. Accordingly,for applications requiring a smaller depth of current penetration, oneor more active electrodes of smaller dimensions would be selected.Conversely, for applications requiring a greater depth of currentpenetration, one or more active electrodes of larger dimensions would beselected.

FIGS. 16-18 illustrate an alternative electrosurgical system 300specifically configured for endoscopic discectomy procedures, e.g., fortreating extruded or non-extruded herniated discs. As shown in FIG. 16system 300 includes a trocar cannula 302 for introducing a catheterassembly 304 through a percutaneous penetration in the patient to atarget disc in the patient's spine. As discussed above, the catheterassembly 304 may be introduced through the thorax in a thoracoscopicprocedure, through the abdomen in a laparascopic procedure, or directlythrough the patient's back. Catheter assembly 304 includes a catheterbody 306 with a plurality of inner lumens (not shown) and a proximal hub308 for receiving the various instruments that will pass throughcatheter body 306 to the target site. In this embodiment, assembly 304includes an electrosurgical instrument 310 with a flexible shaft 312, anaspiration catheter 314, an endoscope 316 and an illumination fibershaft 318 for viewing the target site. As shown in FIGS. 16 and 17,aspiration catheter 314 includes a distal port 320 and a proximalfitment 322 for attaching catheter 314 to a source of vacuum (notshown). Endoscope 316 will usually comprise a thin metal tube 317 with alens 324 at the distal end, and an eyepiece (not shown) at the proximalend.

In the exemplary embodiment, electrosurgical instrument 310 includes atwist locking stop 330 at a proximal end of the shaft 312 forcontrolling the axial travel distance T_(D) of the probe. As discussedin detail below, this configuration allows the surgeon to “set” thedistance of ablation within the disc. In addition, instrument 310includes a rotational indicator 334 for displaying the rotationalposition of the distal portion of instrument 310 to the surgeon. Thisrotational indicator 334 allows the surgeon to view this rotationalposition without relying on the endoscope 316 if visualization isdifficult, or if an endoscope is not being used in the procedure.

Referring now to FIG. 17, a distal portion 340 of electrosurgicalinstrument 310 and catheter body 306 will now be described. As shown,instrument 310 comprises a relatively stiff, but deflectableelectrically insulating support cannula 312 and a working end portion348 movably coupled to cannula 312 for rotational and translationalmovement of working end 348. Working end 348 of electrosurgicalinstrument 310 can be rotated and translated to ablate and remove avolume of nucleus pulposus within a disc. Support cannula 312 extendsthrough an internal lumen 344 and beyond the distal end 346 of catheterbody 306. Alternatively, support cannula 312 may be separate frominstrument 310, or even an integral part of catheter body 306. Thedistal portion of working end 348 includes an exposed return electrode350 separated from an active electrode array 352 by an insulatingsupport member 354, such as ceramic. In the representative embodiment,electrode array 352 is disposed on only one side of ceramic supportmember 354 so that its other side is insulating and thus atraumatic totissue. Instrument 310 will also include a fluid lumen (not shown)having a distal port 360 in working end 348 for delivering electricallyconductive fluid to the target site.

In use, trocar cannula 302 is introduced into a percutaneous penetrationsuitable for endoscopic delivery to the target disc in the spine. Atrephine (not shown) or other conventional instrument may be used toform a channel from the trocar cannula 302 through the annulus fibrosis370 and into the nucleus pulposus. Alternatively, the probe 310 may beused for this purpose, as discussed above. The working end 348 ofinstrument 310 is then advanced through cannula 302 a short distance(e.g., about 7 to 10 mm) into the nucleus pulposus 372, as shown in FIG.18. Once the electrode array 352 is in position, electrically conductivefluid is delivered through distal port 360 to immerse the activeelectrode array 352 in the fluid. The vacuum source may also beactivated to ensure a flow of conductive fluid between electrode array352 past return electrode 350 to suction port 320, if necessary. In someembodiments, the mechanical stop 330 may then be set at the proximal endof the instrument 310 to limit the axial travel distance of working end348. Preferably, this distance will be set to minimize (or completelyeliminate) ablation of the surrounding annulus.

The probe is then energized by applying high frequency voltagedifference between the electrode array 352 and return electrode 350 sothat electric current flows through the conductive fluid from the array352 to the return electrode 350. The electric current causesvaporization of the fluid and ensuing molecular dissociation of thepulposus tissue as described in detail above. The instrument 310 maythen be translated in an axial direction forwards and backwards to thepreset limits. While still energized and translating, the working end348 may also be rotated to ablate tissue surrounding the electrode array352. In the representative embodiment, working end 348 will also includean inflatable gland 380 opposite electrode array 352 to allow deflectionof working end relative to support cannula 312. As shown in FIG. 18,working end 348 may be deflected to produce a large diameter bore withinthe pulposus, which assures close contact with tissue surfaces to beablated. Alternatively, the entire catheter body 306, or the distal endof catheter body 306 may be deflected to increase the volume of pulposusremoved.

After the desired volume of nucleus pulposus is removed (based on directobservation through port 324, or by kinesthetic feedback from movementof working end 348 of instrument 310), instrument 310 is withdrawn intocatheter body 306 and the catheter body is removed from the patient.Typically, the preferred volume of removed tissue is about 0.2 to 5 cm³.

Referring to FIGS. 19-28, alternative systems and methods for ablatingtissue in confined (e.g., narrow) body spaces will now be described.FIG. 19 illustrates an exemplary planar ablation probe 400 according tothe present invention. Similar to the instruments described above, probe400 can be incorporated into electrosurgical system 11 (or othersuitable systems) for operation in either the bipolar or monopolarmodalities. Probe 400 generally includes a support member 402, a distalworking end 404 attached to the distal end of support member 402 and aproximal handle 408 attached to the proximal end of support member 402.As shown in FIG. 19, handle 406 includes a handpiece 408 and a powersource connector 410 removably coupled to handpiece 408 for electricallyconnecting working end 404 with power supply 28 through cable 34 (seeFIG. 1).

In the embodiment shown in FIG. 19, planar ablation probe 400 isconfigured to operate in the bipolar modality. Accordingly, supportmember 402 functions as the return electrode and comprises anelectrically conducting material, such as titanium, or alloys containingone or more of nickel, chromium, iron, cobalt, copper, aluminum,platinum, molybdenum, tungsten, tantalum or carbon. In the preferredembodiment, support member 402 is an austenitic stainless steel alloy,such as stainless steel Type 304 from MicroGroup, Inc., Medway, Mass. Asshown in FIG. 19, support member 402 is substantially covered by aninsulating layer 412 to prevent electric current from damagingsurrounding tissue. An exposed portion 414 of support member 402functions as the return electrode for probe 400. Exposed portion 414 ispreferably spaced proximally from active electrodes 416 by a distance ofabout 1 to 20 mm.

Referring to FIGS. 20 and 21, planar ablation probe 400 furthercomprises a plurality of active electrodes 416 extending from anelectrically insulating spacer 418 at the distal end of support member402. Of course, it will be recognized that probe 400 may include asingle electrode depending on the size of the target tissue to betreated and the accessibility of the treatment site (see FIG. 26, forexample). Insulating spacer 418 is preferably bonded to support member402 with a suitable epoxy adhesive 419 to form a mechanical bond and afluid-tight seal. Electrodes 416 usually extend about 2.0 mm to 20 mmfrom spacer 418, and preferably less than 10 mm. A support tongue 420extends from the distal end of support member 402 to support activeelectrodes 416. Support tongue 420 and active electrodes 416 have asubstantially low profile to facilitate accessing narrow spaces withinthe patient's body, such as the spaces between adjacent vertebrae andbetween articular cartilage and the meniscus in the patient's knee.Accordingly, tongue 420 and electrodes 416 have a substantially planarprofile, usually having a combined height He of less than 4.0 mm,preferably less than 2.0 mm and more preferably less than 1.0 mm (seeFIG. 25). In the case of ablation of meniscus near articular cartilage,the height He of both the tongue 420 and electrodes 416 is preferablybetween about 0.5 to 1.5 mm. The width of electrodes 416 and supporttongue 420 will usually be less than 10.0 mm and preferably betweenabout 2.0 to 4.0 mm.

Support tongue 420 includes a “non-active” surface 422 opposing activeelectrodes 416 covered with an electrically insulating layer (not shown)to minimize undesirable current flow into adjacent tissue or fluids.Non-active surface 422 is preferably atraumatic, i.e., having a smoothplanar surface with rounded corners, to minimize unwanted injury totissue or nerves in contact therewith, such as disc tissue or the nearbyspinal nerves, as the working end of probe 400 is introduced into anarrow, confined body space. Non-active surface 422 of tongue 420 helpto minimize iatrogenic injuries to tissue and nerves so that working end404 of probe 400 can safely access confined spaces within the patient'sbody.

Referring to FIGS. 21 and 22, an electrically insulating support member430 is disposed between support tongue 420 and active electrodes 416 toinhibit or prevent electric current from flowing into tongue 420.Insulating member 430 and insulating layer 412 preferably comprise aceramic, glass or glass ceramic material, such as alumina. Insulatingmember 430 is mechanically bonded to support tongue 420 with a suitableepoxy adhesive to electrically insulate active electrodes 416 fromtongue 420. As shown in FIG. 26, insulating member 430 may overhangsupport tongue 420 to increase the electrical path length between theactive electrodes 416 and the insulation covered support tongue 420.

As shown in FIGS. 21-23, active electrodes 416 are preferablyconstructed from a hollow, round tube, with at least the distal portion432 of electrodes 416 being filed off to form a semi-cylindrical tubewith first and second ends 440, 442 facing away from support tongue 420.Preferably, the proximal portion 434 of electrodes 416 will remaincylindrical to facilitate the formation of a crimp-type electricalconnection between active electrodes 416 and lead wires 450 (see FIG.23). As shown in FIG. 26, cylindrical proximal portions 434 ofelectrodes 416 extend beyond spacer 418 by a slight distance of 0.1 mmto 0.4 mm. The semi-cylindrical configuration of distal electrodeportion 432 increases the electric field intensity and associatedcurrent density around the edges of ends 440, 442, as discussed above.Alternatively, active electrodes 416 may have any of the shapes andconfigurations described above or other configurations, such as squarewires, triangular shaped wires, U-shaped or channel shaped wires and thelike. In addition, the surface of active electrodes 416 may beroughened, e.g., by grit blasting, chemical or electrochemical etching,to further increase the electric field intensity and associated currentdensity around distal portions 432 of electrodes 416.

As shown in FIG. 24, each lead wire 450 terminates at a connector pin452 contained in a pin insulator block 454 within handpiece 408. Leadwires 450 are covered with an insulation layer (not shown), e.g.,Tefzel™, and sealed from the inner portion of support member 402 with anadhesive seal 457 (FIG. 22). In the preferred embodiment, each electrode416 is coupled to a separate source of voltage within power supply 28.To that end, connector pins 452 are removably coupled to matingreceptacles 456 within connector 410 to provide electrical communicationwith active electrodes 416 and power supply 28 (FIG. 1). Electricallyinsulated lead wires 458 connect receptacles 456 to the correspondingsources of voltage within power supply 28. The electrically conductivewall 414 of support member 402 serves as the return electrode, and issuitably coupled to one of the lead wires 450.

In an alternative embodiment, adjacent electrodes 416 may be connectedto the opposite polarity of source 28 so that current flows betweenadjacent active electrodes 416 rather than between active electrodes 416and return electrode 414. By way of example, FIG. 21B illustrates adistal portion of a planar ablation probe 400′ in which electrodes 416 aand 416 c are at one voltage polarity (i.e., positive) and electrodes416 b and 416 d are at the opposite voltage polarity (negative). When ahigh frequency voltage is applied between electrodes 416 a, 416 c andelectrodes 416 b, 416 d in the presence of electrically conductingliquid, current flows between electrodes 416 a, 416 c and 416 b, 416 das illustrated by current flux lines 522′. Similar to the aboveembodiments, the opposite surface 420 of working end 404′ of probe 400′is generally atraumatic and electrically insulated from activeelectrodes 416 a, 416 b, 416 c and 416 d to minimize unwanted injury totissue in contact therewith.

In an exemplary configuration, each source of voltage includes a currentlimiting element or circuitry (not shown) to provide independent currentlimiting based on the impedance between each individual electrode 416and return electrode 414. The current limiting elements may be containedwithin the power supply 28, the lead wires 450, cable 34, handle 406, orwithin portions of the support member 402 distal to handle 406. By wayof example, the current limiting elements may include resistors,capacitors, inductors, or a combination thereof. Alternatively, thecurrent limiting function may be performed by (1) a current sensingcircuit which causes the interruption of current flow if the currentflow to the electrode exceeds a predetermined value and/or (2) animpedance sensing circuit which causes the interruption of current flow(or reduces the applied voltage to zero) if the measured impedance isbelow a predetermined value. In another embodiment, two or more of theelectrodes 416 may be connected to a single lead wire 450 such that allof the electrodes 416 are always at the same applied voltage relative toreturn electrode 414. Accordingly, any current limiting elements orcircuits will modulate the current supplied or the voltage applied tothe array of electrodes 416, rather than limiting their currentindividually, as discussed in the previous embodiment.

Referring to FIGS. 25-28, methods for ablating tissue structures withplanar ablation probe 400 according to the present invention will now bedescribed. In particular, exemplary methods for treating a diseasedmeniscus within the knee (FIGS. 29-31) and for removing soft tissuebetween adjacent vertebrae in the spine (FIG. 32) will be described. Inboth procedures, at least the working end 404 of planar ablation probe400 is introduced to a treatment site either by minimally invasivetechniques or open surgery. Electrically conducting liquid is deliveredto the treatment site, and voltage is applied from power supply 28between active electrodes 416 and return electrode 414. The voltage ispreferably sufficient to generate electric field intensities near activeelectrodes that form a vapor layer in the electrically conductingliquid, and induce the discharge of energy from the vapor layer toablate tissue at the treatment site, as described in detail above.

Referring to FIG. 25, working end 404 and at least the distal portion ofsupport member 402 are introduced through a percutaneous penetration500, such as a cannula, into the arthroscopic cavity 502. The insertionof probe 400 is usually guided by an arthroscope (not shown) whichincludes a light source and a video camera to allow the surgeon toselectively visualize a zone within the knee joint. To maintain a clearfield of view and to facilitate the generation of a vapor layer, atransparent, electrically conductive irrigant 503, such as isotonicsaline, is injected into the treatment site either through a liquidpassage in support member 402 of probe 400, or through anotherinstrument. Suitable methods for delivering irrigant to a treatment siteare described in commonly assigned, co-pending application U.S. Pat. No.5,697,281 filed on Jun. 7, 1995, previously incorporated herein byreference.

In the example shown in FIG. 25, the target tissue is a portion of themeniscus 506 adjacent to and in close proximity with the articularcartilage 510, 508 which normally covers the end surfaces of the tibia512 and the femur 514, respectively. The articular cartilage 508, 510 isimportant to the normal functioning of joints, and once damaged, thebody is generally not capable of regenerating this critical lining ofthe joints. Consequently, it is desirable that the surgeon exerciseextreme care when treating the nearby meniscus 506 to avoid unwanteddamage to the articular cartilage 508, 510. The confined spaces 513between articular cartilage 508, 510 and meniscus 506 within the kneejoint are relatively narrow, typically on the order of about 1.0 mm to5.0 mm. Accordingly, the narrow, low profile working end 404 of ablationprobe 400 is ideally suited for introduction into these confined spaces513 to the treatment site. As mentioned previously, the substantiallyplanar arrangement of electrodes 416 and support tongue 420 (typicallyhaving a combined height of about 0.5 to 1.5 mm) allows the surgeon todeliver working end 404 of probe 400 into the confined spaces 513, whileminimizing contact with the articular cartilage 508, 510 (see FIG. 26).

As shown in FIG. 26, active electrodes 416 are disposed on one face ofworking end 404 of probe 400. Accordingly, a zone 520 of high electricfield intensity is generated on each electrode 416 on one face ofworking end 404 while the opposite side 521 of working end 404 isatraumatic with respect to tissue. In addition, the opposite side 521 isinsulated from electrodes 416 to minimize electric current from passingthrough this side 521 to the tissue (i.e., adjacent articular cartilage508). As shown in FIGS. 26, the bipolar arrangement of active electrodes416 and return electrode 414 causes electric current to flow along fluxlines 522 predominantly through the electrically conducting irrigant503, which envelops the tissue and working end 404 of ablation probe 400and provides an electrically conducting path between electrodes 416 andreturn electrode 414. As electrodes 416 are engaged with, or positionedin close proximity to, the target meniscus 506, the high electric fieldpresent at the electrode edges cause controlled ablation of the tissueby forming a vapor layer and inducing the discharge of energy therefrom.In addition, the motion of electrodes 416 relative to the meniscus 506(as shown by vector 523) causes tissue to be removed in a controlledmanner. The presence of the irrigant also serves to minimize theincrease in the temperature of the meniscus during the ablation processbecause the irrigant generally comes in contact with the treated tissueshortly after one of the electrodes 416 has been translated across thesurface of the tissue.

Referring now to FIG. 28, an exemplary method for removing soft tissue540 from the surfaces of adjacent vertebrae 542, 544 in the spine willnow be described. Removal of this soft tissue 540 is often necessary,for example, in surgical procedures for fusing or joining adjacentvertebrae together. Following the removal of tissue 540, the adjacentvertebrae 542, 544 are stabilized to allow for subsequent fusiontogether to form a single monolithic vertebra. As shown, the low-profileof working end 404 of probe 400 (i.e., thickness values as low as 0.2mm) allows access to and surface preparation of closely spacedvertebrae. In addition, the shaped electrodes 416 promote substantiallyhigh electric field intensities and associated current densities betweenactive electrodes 416 and return electrode 414 to allow for theefficient removal of tissue attached to the surface of bone withoutsignificantly damaging the underlying bone. The “non-active” insulatingside 521 of working end 404 also minimizes the generation of electricfields on this side 521 to reduce ablation of the adjacent vertebra 542.

The target tissue is generally not completely immersed in electricallyconductive liquid during surgical procedures within the spine, such asthe removal of soft tissue described above. Accordingly, electricallyconducting liquid will preferably be delivered into the confined spaces513 between adjacent vertebrae 542, 544 during this procedure. The fluidmay be delivered through a liquid passage (not shown) within supportmember 402 of probe 400, or through another suitable liquid supplyinstrument.

Other modifications and variations can be made to disclose embodimentswithout departing from the subject invention as defined in the followingclaims. For example, it should be clearly understood that the planarablation probe 400 described above may incorporate a single activeelectrode, rather than a plurality of such active electrodes asdescribed above in the exemplary embodiment. FIG. 27 illustrates aportion of a planar ablation probe according to the present inventionthat incorporates a single active electrode 416′ for generating highelectric field densities 550 to ablate a target tissue 552. Electrode416′ may extend directly from a proximal support member, as depicted inFIG. 31, or it may be supported on an underlying support tongue (notshown) as described in the previous embodiment. As shown, therepresentative single active electrode 416′ has a semi-cylindricalcross-section, similar to the electrodes 416 described above. However,the single electrode 416′ may also incorporate any of the abovedescribed configurations (e.g., square or star shaped solid wire) orother specialized configurations depending on the function of thedevice.

Referring now to FIGS. 29-31 an alternative electrode support member 500for a planar ablation probe 404 will be described in detail. As shown,electrode support member 500 preferably comprises a multilayer or singlelayer substrate 502 comprising a suitable high temperature, electricallyinsulating material, such as ceramic. The substrate 502 is a thin orthick film hybrid having conductive strips that are adhered to, e.g.,plated onto, the ceramic wafer. The conductive strips typically comprisetungsten, gold, nickel or equivalent materials. In the exemplaryembodiment, the conductive strips comprise tungsten, and they areco-fired together with the wafer layers to form an integral package. Theconductive strips are coupled to external wire connectors by holes orvias that are drilled through the ceramic layers, and plated orotherwise covered with conductive material.

In the representative embodiment, support member 500 comprises a singleceramic wafer having a plurality of longitudinal ridges 504 formed onone side of the wafer 502. Typically, the wafer 502 is green pressed andfired to form the required topography (e.g., ridges 504). A conductivematerial is then adhered to the ridges 502 to form conductive strips 506extending axially over wafer 502 and spaced from each other. As shown inFIG. 31, the conductive strips 506 are attached to lead wires 508 withinshaft 412 of the probe 404 to electrically couple conductive strips 506with the power supply 28 (FIG. 1). This embodiment provides a relativelylow profile working end of probe 404 that has sufficient mechanicalstructure to withstand bending forces during the procedure.

FIGS. 34-36 illustrate another system and method for treating swollen orherniated spinal discs according to the present invention. In thisprocedure, an electrosurgical probe 700 comprises a long, thin shaft 702(e.g., on the order of about 1 mm in diameter or less) that can bepercutaneously introduced anteriorly through the abdomen or thorax, orthrough the patient's back directly into the spine. The probe shaft 702will include one or more active electrode(s) 704 for applying electricalenergy to tissues within the spine. The probe 700 may include one ormore return electrode(s) 706, or the return electrode may be positionedon the patient's back, as a dispersive pad (not shown).

As shown in FIG. 34, the distal portion of shaft 702 is introducedanteriorly through a small percutaneous penetration into the annulus 710of the target spinal disc. To facilitate this process, the distal end ofshaft 702 may taper down to a sharper point (e.g., a needle), which canthen be retracted to expose active electrode(s) 704. Alternatively, theelectrodes may be formed around the surface of the tapered distalportion of shaft (not shown). In either embodiment, the distal end ofshaft is delivered through the annulus 710 to the target nucleuspulposus 290, which may be herniated, extruded, non-extruded, or simplyswollen. As shown in FIG. 35, high frequency voltage is applied betweenactive electrode(s) 704 and return electrode(s) 710 to heat thesurrounding collagen to suitable temperatures for contraction (i.e.,typically about 55° C. to about 70° C.). As discussed above, thisprocedure may be accomplished with a monopolar configuration, as well.However, applicant has found that the bipolar configuration shown inFIGS. 34-36 provides enhanced control of the high frequency current,which reduces the risk of spinal nerve damage.

As shown in FIGS. 35 and 36, once the nucleus pulposus 290 has beensufficiently contracted to retract from impingement on the nerve 720,the probe 700 is removed from the target site. In the representativeembodiment, the high frequency voltage is applied between active andreturn electrode(s) 704 706 as the probe is withdrawn through theannulus 710. This voltage is sufficient to cause contraction of thecollagen fibers within the annulus 710, which allows the annulus 710 tocontract around the hole formed by probe 700, thereby improving thehealing of this hole. Thus, the probe 700 seals its own passage as it iswithdrawn from the disc.

In yet another aspect, the systems and devices of the present inventioncan be used to treat and seal fissures (or tears) on the annulusfibrosus of an intervertebral disc 730. As illustrated in FIG. 37,annulus fibrosus 732 can form fissures 734 along its inner surface 738,outer surface 740, or the fissures can be formed throughout the innerportion of annulus fibrosus 732 such that they extend circumferentiallyaround a portion of the disc (not shown). Spinal nerves can grow intothe fissures, which can lead to irritation and pain. Moreover, if leftuntreated, the fissures can propagate and can eventually lead to thepartial or complete herniation of the disc, which may result in the discimpinging on surrounding nerves.

FIG. 38 illustrates an anterior endoscopic method of the presentinvention. Of course, it will be recognized that the present inventioncan be used with a variety of different access techniques, includingopen, endoscopic or percutaneous procedures, as well as anterior,posterior, or lateral approaches. FIG. 38 illustrates an endoscopictechnique which may be part of a microendoscopy procedure. Asillustrated, a surgical instrument 300 can be introduced through atrocar cannula 302 for percutaneous insertion to a target disc 730. Oncethe target disc has been accessed, instrument 300 is positioned suchthat its distal end is in close proximity or in contact with fissure734. The fissure may be accessed with a posterior approach (not shown),or the anterior approach shown. In the latter case, instrument 300 canbe advanced either directly through nucleus pulposus 735, or asemiflexible probe can be guided around the annulus 732 or snaked alongthe inner surface 736 of the annulus to the fissure. Once activeelectrode(s) 740 are in position adjacent fissure 734, a power supply(not shown) is activated so that an appropriate high frequency voltageis applied between the active electrode(s) 740 and return electrode(s)742 to heat and seal fissure 734.

Once annulus 732 has been sufficiently treated to substantially sealfissure 734, probe 20 is removed from the target disc. In therepresentative embodiment, the high frequency voltage is applied betweenactive electrode 740 and return electrode(s) 742. This voltage issufficient to cause contraction of the collagen fibers within theannulus 732, which allows the annulus to contract around the hole formedby probe 20, thereby improving the healing of this hole.

In a specific configuration, an electrically conductive fluid isdelivered to immerse active electrode 740 and fissure 734 in the fluidto provide a conductive path between the active electrode(s) and thereturn electrode. The electrically conductive fluid may be a gas orliquid such as isotonic saline, delivered to the target site, or aviscous fluid, such as a gel, that is located at the target site. Theprobe is energized by applying a high frequency voltage differencebetween the active electrode and the return electrode so that electriccurrent flows through the conductive fluid from the active electrode tothe return electrode. In some embodiments, the high frequency voltage issufficient to convert the electrically conductive fluid between thefissure and the active electrode into an ionized vapor layer or plasma.In other embodiments, the voltage is insufficient to form such a plasma.In these embodiments, the voltage generates heat, either directly in thetissue or in the fluid, that is sufficient to heat and seal the fissure.The voltage difference between the active electrodes and the returnelectrode typically elevates the tissue temperature from normal bodytemperatures (e.g., 37° C.) to temperatures in the range of 45° C. to90° C., preferably in the range from 60° C. to 70° C. Applicants believethat this temperature elevation causes thermal contraction or shrinkageof the collagen connective fibers within the annulus tissue surroundingthe fissure and/or a thermal bonding of the annulus tissue.

Preferably, return electrode 742 is positioned proximal from the activeelectrode 740 to draw the electric current away from the tissue site tolimit the depth of penetration of the current into the tissue, therebyinhibiting molecular dissociation and breakdown of the collagen tissueand minimizing or completely avoiding damage to surrounding andunderlying tissue structures beyond fissure 732. In an exemplaryembodiment, the active electrode(s) 742 are held away from the tissue asufficient distance such that the RF current does not pass into thetissue at all, but rather passes through the electrically conductingfluid back to the return electrode. In this embodiment, the primarymechanism for imparting energy to the tissue is the heated conductivefluid, rather than the electric current.

In alternative embodiments, the active electrode(s) are brought intocontact with, or close proximity to, the target tissue so that theelectric current passes directly into the tissue to a selected depth. Inthese embodiments, the return electrode draws the electric current awayfrom the tissue site to limit its depth of penetration into the tissue.Applicants have discovered that the depth of current penetration alsocan be varied with the electrosurgical system of the present inventionby changing the frequency of the voltage applied to the active electrodeand the return electrode. This is because the electrical impedance oftissue is known to decrease with increasing frequency due to theelectrical properties of cell membranes which surround electricallyconductive cellular fluid. At lower frequencies (e.g., less than 350kHz), the higher tissue impedance, the presence of the return electrodeand the active electrode configuration of the present invention(discussed in detail below) cause the current flux lines to penetrateless deeply resulting in a smaller depth of tissue heating. In anexemplary embodiment, an operating frequency of about 100 to 200 kHz isapplied to the active electrode(s) to obtain shallow depths of tissueheating (e.g., usually less than 1.5 mm and preferably less than 0.5mm).

While the above figures show sealing fissures along an outer surface ofannulus 732, it will be appreciated that the method of the presentinvention can be used to seal fissures on the inner surface of annulus732, as illustrated in FIG. 39.

Similar to the above described probes, the electrosurgical probe orcatheter will comprise a shaft or a handpiece having a proximal end anda distal end which supports the active electrode(s). The shaft orhandpiece may assume a wide variety of configurations, with the primarypurpose being to mechanically support the active electrode and permitthe treating physician to manipulate the electrode from a proximal endof the shaft. The shaft may be rigid or flexible, with flexible shaftsoptionally being combined with a generally rigid external tube formechanical support. Flexible shafts may be combined with pull wires,shape memory actuators, and other known mechanisms for effectingselective deflection of the distal end of the shaft to facilitatepositioning of the electrode array. The shaft will usually include aplurality of wires or other conductive elements running axiallytherethrough to permit connection of the electrode array to a connectorat the proximal end of the shaft.

The shaft will have a suitable diameter and length to allow the surgeonto reach the fissure by delivering the shaft through the thoraciccavity, the abdomen, or the like. Thus, the shaft will usually have alength in the range of about 5.0 to 30.0 cm, and a diameter in the rangeof about 0.2 mm to about 20 mm. Alternatively, the shaft may bedelivered directly through the patient's back in a posterior approach,which would considerably reduce the required length of the shaft. In anyof these embodiments, the shaft may also be introduced through rigid orflexible endoscopes.

The voltage applied between the return electrode(s) and the activeelectrode array will be at high or radio frequency, typically betweenabout 5 kHz and 20 MHz, usually being between about 30 kHz and 2.5 MHz,preferably being between about 50 kHz and 500 kHz, more preferably lessthan 350 kHz, and most preferably between about 100 kHz and 200 kHz. TheRMS (root mean square) voltage applied will usually be in the range fromabout 5 volts to 1000 volts, preferably being in the range from about 10volts to 500 volts depending on the active electrode size, the operatingfrequency and the operation mode of the particular procedure or desiredeffect on the tissue (i.e., contraction or coagulation). Typically, thepeak-to-peak voltage will be in the range of 10 to 2000 volts,preferably in the range of 20 to 1200 volts and more preferably in therange of about 40 to 800 volts (again, depending on the electrode size,the operating frequency and the operation mode).

As discussed above, the voltage is usually delivered in a series ofvoltage pulses or alternating current of time varying voltage amplitudewith a sufficiently high frequency (e.g., on the order of 5 kHz to 20MHz) such that the voltage is effectively applied continuously (ascompared with e.g., lasers claiming small depths of necrosis, which aregenerally pulsed about 10 to 20 Hz). In addition, the duty cycle (i.e.,cumulative time in any one-second interval that energy is applied) is onthe order of about 50% for the present invention, as compared withpulsed lasers which typically have a duty cycle of about 0.0001%.

The preferred power source of the present invention delivers a highfrequency current selectable to generate average power levels rangingfrom several milliwatts to tens of watts per electrode, depending on thevolume of target tissue being heated, and/or the maximum allowedtemperature selected for the probe tip.

In the representative embodiment, the power supply will apply a voltageof about 150 to 600 volts rms between the active and return electrodes,and the voltage reduction element will reduce this voltage to about 20to 300 volts rms to the active electrode. In this manner, the voltagedelivered to the active electrode is below the threshold for ablation oftissue, but high enough to heat and seal the fissure.

The present invention may use a single active electrode or an electrodearray extending from an electrically insulating support member,typically made of an inorganic material such as ceramic, silicone orglass. The active electrode will usually have a smaller exposed surfacearea than the return electrode such that the current densities are muchhigher at the active electrode than at the other electrodes. Preferably,the return electrode has a relatively large, smooth surfaces extendingaround the instrument shaft to reduce current densities, therebyminimizing damage to adjacent tissue.

The electrode array usually includes a plurality of independentlycurrent-limited and/or power-controlled active electrodes to applyelectrical energy selectively to the fissure while limiting the unwantedapplication of electrical energy to the surrounding annulus tissue andenvironment resulting from power dissipation into surroundingelectrically conductive liquids, such as the nucleus pulposus, blood,normal saline, electrically conductive gel, and the like. Alternatively,the active electrodes may be connected to each other at either theproximal or distal ends of the probe to form a single wire that couplesto a power source.

In some embodiments, the active electrode(s) have an active portion orsurface with surface geometries shaped to promote the electric fieldintensity and associated current density along the leading edges of theelectrodes. Suitable surface geometries may be obtained by creatingelectrode shapes that include preferential sharp edges, or by creatingasperities or other surface roughness on the active surface(s) of theelectrodes. Electrode shapes according to the present invention caninclude the use of formed wire (e.g., by drawing round wire through ashaping die) to form electrodes with a variety of cross-sectionalshapes, such as square, rectangular, L or V shaped, or the like.Electrode edges may also be created by removing a portion of theelongate metal electrode to reshape the cross-section. For example,material can be removed at closely spaced intervals along the electrodelength to form transverse grooves, slots, threads or the like along theelectrodes.

Additionally or alternatively, the active electrode surface(s) may bemodified through chemical, electrochemical or abrasive methods to createa multiplicity of surface asperities on the electrode surface. Thesesurface asperities will promote high electric field intensities betweenthe active electrode surface(s) and the target tissue to facilitateablation or cutting of the tissue. For example, surface asperities maybe created by etching the active electrodes with etchants having a Phless than 7.0 or by using a high velocity stream of abrasive particles(e.g., grit blasting) to create asperities on the surface of anelongated electrode.

The tip region of the probe may comprise many independent activeelectrodes designed to deliver electrical energy in the vicinity of thetip. The selective application of electrical energy to the conductivefluid is achieved by connecting each individual active electrode and thereturn electrode to a power source having independently controlled orcurrent limited channels. The return electrode(s) may comprise a singletubular member of conductive material proximal to the electrode array atthe tip which also serves as a conduit for the supply of theelectrically conducting fluid between the active and return electrodes.Alternatively, the probe may comprise an array of return electrodes atthe distal tip of the probe (together with the active electrodes) tomaintain the electric current at the tip. The application of highfrequency voltage between the return electrode(s) and the electrodearray results in the generation of high electric field intensities atthe distal tips of the active electrodes with conduction of highfrequency current from each individual active electrode to the returnelectrode. The current flow from each individual active electrode to thereturn electrode(s) is controlled by either active or passive means, ora combination thereof, to deliver electrical energy to the surroundingconductive fluid while minimizing energy delivery to surrounding annulus(e.g. non-target) tissue.

The tissue volume over which energy is dissipated (i.e., a high currentdensity exists) may be precisely controlled, for example, by the use ofa multiplicity of small active electrodes whose effective diameters orprincipal dimensions range from about 5 mm to 0.01 mm, preferably fromabout 2 mm to 0.05 mm, and more preferably from about 1 mm to 0.1 mm.Electrode areas for both circular and non-circular electrodes will havea contact area (per active electrode) below 25 mm², preferably being inthe range from 0.0001 mm to 1 mm², and more preferably from 0.005 mm² to0.5 mm². The circumscribed area of the electrode array is in the rangefrom 0.25 mm² to 200 mm², preferably from 0.5 mm² to 100 mm², and willusually include at least two isolated active electrodes, preferably atleast five active electrodes, often greater than 10 active electrodesand even 50 or more active electrodes, disposed over the distal contactsurfaces on the shaft. The use of small diameter active electrodesincreases the electric field intensity and reduces the extent or depthof collateral tissue heating as a consequence of the divergence ofcurrent flux lines which emanate from the exposed surface of each activeelectrode.

Applicants have found that the thin electrode array 754 configuration ofelectrosurgical probe 750 of FIG. 40 provides an exemplary interface tofocus energy on the fissure 734, which is typically substantially linearover at least a portion of the fissure. The thin electrode arraypromotes localized electric fields between the electrodes and thefissure. The use of the thin electrode array increases the electricfield intensity and reduces the extent or depth of collateral tissueheating as a consequence of the divergence of current flux lines whichemanate from the exposed surface of the active electrodes. As a result,the linear electrode array can improve the sealing of the fissure andreduce the collateral damage to the surrounding tissue.

Each of the above systems may also include a vacuum source (not shown)for coupling to a suction lumen or tube (see FIG. 2) in the probe foraspirating the target site. In some procedures, it may also be necessaryto retrieve or aspirate the electrically conductive fluid after it hasbeen directed to the fissure. Accordingly, the system of the presentinvention will usually include a suction lumen in the probe, or onanother instrument, for aspirating fluids from the fissure. The probeoften comprises a central opening 209 which is coupled to a suction oraspiration lumen (see FIG. 2) within shaft 100 and a suction tube 211(FIG. 2) for aspirating tissue, fluids and/or gases from the targetsite. In some embodiments, the electrically conductive fluid generallyflows from opening 237 of fluid tube 239 radially inward past activeelectrodes 104 and then back through the central opening 209 of supportmember 102. Aspirating the electrically conductive fluid during surgeryallows the surgeon to see the target site, and it prevents the fluidfrom flowing into the patient's body, e.g., into the nucleus pulposus,the abdomen or the thoracic cavity. This aspiration should becontrolled, however, so that the conductive fluid maintains a conductivepath between the active electrode(s) and the return electrode.

Other modifications and variations can be made to disclose embodimentswithout departing from the subject invention as defined in the followingclaims. For example, it should be noted that the invention is notlimited to an electrode array comprising a plurality of activeelectrodes. The invention could utilize a plurality of returnelectrodes, e.g., in a bipolar array or the like. In addition, dependingon other conditions, such as the peak-to-peak voltage, electrodediameter, etc., a single active electrode may be sufficient to contractcollagen tissue, ablate tissue, treat fissures, or the like.

In addition, the active and return electrodes may both be located on adistal tissue treatment surface adjacent to each other. The active andreturn electrodes may be located in active/return electrode pairs, orone or more return electrodes may be located on the distal tip togetherwith a plurality of electrically isolated active electrodes. Theproximal return electrode may or may not be employed in theseembodiments. For example, if it is desired to maintain the current fluxlines around the distal tip of the probe, the proximal return electrodewill not be desired.

What is claimed is:
 1. A method of treating a fissure in anintervertebral disc comprising: positioning an active electrode adjacentan outer surface of an annulus surrounding an intervertebral disc;delivering a sealant to a fissure within the annulus; and applying ahigh frequency voltage difference between the active electrode and areturn electrode, the voltage difference being sufficient tosubstantially seal the fissure within the annulus.
 2. The method ofclaim 1 further comprising positioning the active electrode in anelectrically conductive fluid.
 3. The method of claim 2 wherein theelectrically conductive fluid is isotonic saline.
 4. The method of claim2 wherein the active electrode and the return electrode are submersedwithin the electrically conductive fluid.
 5. The method of claim 2wherein the electrically conductive fluid is a viscous gel.
 6. Themethod of claim 5 comprising heating the electrically conductive gel toheat the tissue surrounding the fissure.
 7. The method of claim 2comprising generating electric field intensities between the activeelectrode and the return electrode such that the electric fieldintensities are sufficient to vaporize at least a portion of the fluidin contact with the active electrode.
 8. The method of claim 7 furthercomprising accelerating charged particles from the vaporized fluid tothe tissue immediately surrounding the fissure to cause heating.
 9. Themethod of claim 2 wherein the applying step is carried out by directingan electrical current through the electrically conductive fluid and intoa tissue surrounding the fissure.
 10. The method of claim 9 wherein theelectrical current passes only through the electrically conductive fluidto heat the fissure.
 11. The method of claim 2 comprising positioningthe return electrode within the electrically conductive fluid tocomplete a current flow path between the active electrode and the returnelectrode.
 12. The method of claim 2 comprising directing theelectrically conductive fluid along a fluid path past the returnelectrode and active electrode to the fissure.
 13. The method of claim 2further comprising aspirating at least a portion of the electricallyconductive fluid.
 14. The method of claim 1 wherein the positioning stepis carried out by placing the active electrode closer to the fissurethan the return electrode.
 15. The method of claim 1 comprising limitinga depth of penetration of an electrical current by drawing theelectrical current from the active electrode toward the returnelectrode.
 16. The method of claim 1 wherein the applying step elevatesthe temperature of the tissue adjacent to the fissure to a temperaturebetween approximately 45° C. and 90° C.
 17. The method of claim 1wherein the applying step elevates the temperature of the tissueadjacent the fissure to a temperature between approximately 60° C. and70° C.
 18. The method of claim 1 wherein the act of applying a highfrequency voltage difference between the active and return electrodecomprises heating the collagen fibers within the annulus by passing anelectric current into the collagen fibers.
 19. The method of claim 1wherein the applying step is carried out with RF electrical energy. 20.The method of claim 1 wherein the sealant is chosen from a groupcomprising fibrogen glue and collagen.
 21. The method of claim 1 furthercomprising positioning the return electrode on the outer surface of thepatient's body, and conducting electrical current from the activeelectrode, through the patient's body, to the return electrode.
 22. Themethod of claim 1 wherein the active electrode comprises a single,active electrode at the distal end of a shaft.
 23. The method of claim 1wherein the active electrode comprises a plurality of electricallyisolated active electrodes at the distal end of a shaft.
 24. The methodof claim 23 wherein the active electrodes are linear.
 25. The method ofclaim 1 further comprising independently controlling current flow fromthe active electrode based on impedance between the active electrode andthe return electrode.
 26. The method of claim 1 wherein the returnelectrode is axially spaced from the active electrode.
 27. A method oftreating an intervertebral disc comprising: delivering a sealant to afissure within an annulus fibrosus surrounding the intervertebral disc;positioning an active electrode adjacent an outer surface of the annulusfibrosus; directing a conducting fluid between the active electrode andthe annulus; and applying sufficient high frequency electrical energy tothe active electrode to heat and seal a fissure in the annulus.
 28. Themethod of claim 27 wherein the positioning step further comprisesintroducing at least a distal end of an electrosurgical instrumentthrough a percutaneous penetration in a patient.
 29. The method of claim28 wherein the percutaneous penetration is located on the patient'sback, abdomen, or thorax.
 30. The method of claim 29 further comprisingadvancing the active electrode through the annulus fibrosus and into anucleus pulposus.
 31. The method of claim 27 further comprisingpositioning the active electrode and a return electrode within anelectrically conductive fluid to generate an electrically conductivepath therebetween.
 32. An electrosurgical system for treating a fissurewithin an annulus fibrosus comprising: a shaft having a proximal endportion and a distal end portion, the distal end portion beingconfigured for introduction to an outer surface of an annulus in closeproximity to, or in contact with, a fissure in the annulus; an activeelectrode disposed on the distal end portion of the shaft; a returnelectrode; a high frequency voltage source adapted to generate a voltagesufficient to seal the fissure, the high frequency voltage source inelectrical communication with the active and return electrodes; and asealant delivery element for delivering a sealant to the fissure. 33.The system of claim 32 further comprising a fluid delivery element forsupplying electrically conductive fluid to the fissure to substantiallysurround at least the active electrode with the fluid and to locate thefluid between the active electrode and the fissure.
 34. The system ofclaim 33 wherein the fluid delivery element defines a fluid path inelectrical contact with the return electrode and the active electrode togenerate a current flow path between the return electrode and the activeelectrode.
 35. The system of claim 33 wherein the fluid delivery elementcomprises a fluid tube extending along an outer surface of the shaft,the tube having an inlet positioned proximal to the return electrode,wherein the return electrode is spaced proximally from the activeelectrode.
 36. The system of claim 33 wherein the fluid delivery elementcomprises a fluid supply instrument separate from the electrosurgicalprobe.
 37. The system of claim 32 wherein the distal end portion of theshaft has a diameter less than about 2.0 mm.
 38. The system of claim 32wherein the return electrode is disposed proximal of the activeelectrode.
 39. The system of claim 32 further including an insulatingmember positioned between the return electrode and the active electrode,the return electrode being sufficiently spaced from the active electrodeto minimize direct contact between the return electrode and the annuluswhen the active electrode is positioned in close proximity or in partialcontact with the fissure.
 40. The system of claim 32 wherein the activeelectrode comprises an electrode array disposed near the distal endportion of the shaft, the array including a plurality of electricallyisolated active electrodes disposed over a contact surface.
 41. Thesystem of claim 40 wherein the electrode array comprises an edge forpromoting localized electric fields between the edge and the fissure.42. The system of claim 32 wherein the active electrode comprises asingle active electrode disposed near the distal end portion of theshaft.
 43. The system of claim 32 further comprising a fluid aspirationelement.
 44. The system of claim 43 wherein the fluid aspiration elementcomprises a suction lumen extending through the shaft, the suction lumenhaving an inlet at a distal tip of the shaft adjacent the activeelectrode.
 45. The system of claim 43, further comprising an aspirationelectrode in fluid communication with the fluid aspiration element. 46.The system of claim 45, wherein the aspiration electrode comprises anelectrode configuration selected from the group consisting of: at leastone coiled electrode, a wire mesh electrode, a cage electrode, and ascreen electrode.
 47. The system of claim 32 wherein the sealantdelivery element extends down the shaft.
 48. the system of claim 47wherein the voltage is sufficient to heat the sealant within thefissure.
 49. The system of claim 48 wherein the sealant delivery elementcomprise a tube extending along an outer surface of the shaft, the tubehaving an opening positioned adjacent the active electrode, wherein thereturn electrode is spaced proximally from the active electrode.
 50. Thesystem of claim 48 wherein the sealant is chosen from a group comprisingan adhesive, collagen, and fibrogen glue.
 51. The system of claim 48wherein the sealant delivery element is separate from the shaft.